Science Fair Idea: Lens Made of Air

For the student looking for a simple science fair project that will mystify the teacher, you’ve come to the right place. When the teacher asks what scientific question(s) your project will demonstrate, you can propose the following:

Is it possible to construct a convex lens that will have a magnification factor of less than one? Is it possible to construct a concave lens that will have a magnification factor of more than one?

To put it another way, a convex lens (such as the one on the left) makes things look bigger, and a concave lens (shown on the right) makes things look smaller. But your simple experiment will show that it’s possible to make a convex lens that makes things look smaller, and a concave lens that makes them look smaller.

A lens is usually made out of a substance such as glass, which is denser than air. This means that light waves travel more slowly through the lens. But there’s no reason why you have to use glass and air. In your case, you will use air for the lens, and water instead of the air. This means that the speed of light is faster through the lens, rather than slower, as we usually think of lenses.

The layout for the lens is quite simple, as you can see from the illustrations. You need a small can, covered on each side with a piece of cellophane. Any type of clear flexible plastic should work fine. The easiest option is probably cling wrap. You’ll need to cut a hole in the side of the can, and insert a flexible rubber or plastic tube. The connection needs to be air tight. There are probably other ways to make the connection, but the easiest would probably be to use a small brass tube, and solder it to the can. (You’ll need a soldering iron, which probably costs a lot less than you would expect.) Slide the plastic tube over the brass, and make sure the connection is water tight. The construction details are shown at the right.

If you blow into the tube, as shown in the illustration above, then the can becomes a convex lens, made out of air. And if you suck air out of the tube, as shown at the left, it becomes a concave lens. Place it in a container of water, and you can watch how a black stripe at the bottom of the container is magnified or made smaller, but the opposite of how it would work with a glass lens in air.

Your teacher will have to concede that there’s nothing in the definition of “lens” that requires it to be made out of glass. He or she will have little choice but to award you the blue ribbon for answering your questions in the affirmative.

The project appeared 85 years ago this month in the April 1937 issue of Popular Science.

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1947 Phono Maintenance Tips

This young woman enjoyed listening to her record player, but thanks to the hints in the April 1947 issue of Popular Mechanics, she also knew how to take care of it. The record player was designed to withstand rough handling, but it was also a precision instrument that required occasional attention.

For one thing, the wires under the pickup arm could come loose and drag along the record. The magazine explained how to pull the wires tight to prevent this.

If the record player wouldn’t play at all, it was likely the cartridge, and the magazine explained how to replace it. It also explained the importance of cleaning dust off records, as well as the need to occasionally oil the bearings.

Eclipse of April 8, 2024

2024 Eclipse Path. NOAA image.

As we did in 2017, OneTubeRadio.com will provide full coverage of the April 8, 2024, total solar eclipse, which will take place two years from today.

For the 2017 eclipse, hotel rooms and other accommodations started becoming scarce a few months prior to the eclipse. A few rooms remained available up until two weeks prior to the eclipse.

In general, most hotels allow you to make reservations one year in advance. Therefore, if you plan to see the eclipse in an area experiencing totality, which we strongly recommend, then you should plan on booking a hotel room on April 8, 2023. For the 2017 eclipse, we booked a fully refundable hotel room, so there was no risk if we changed our plans. In 2024, we’ll probably view the eclipse in Texas, although our plans are not settled. For the 2019 annular eclipse, we had contingency plans that included both a hotel and campground in Canada, and a campground in the U.S. Since the border was still closed, we cancelled the Canadian reservations, since we made sure to get fully refundable ones.

Speaking of annular eclipses, there is one of those on October 14, 2023. That event, while interesting, is nowhere near as breathtaking as a total eclipse. So if you happen to be close, you should take in the 2023 event. But the 2024 total eclipse is in an entirely different league.

The 2024 total eclipse will be visible in parts of Texas, Oklahoma, Arkansas, Missouri, Illinois, Indiana, Ohio, a tiny piece of Michigan, Pennsylvania, New York, Vermont, New Hampshire, and Maine. The path of totality also passes through Mexico and Canada. Major cities in the path of totality include Dallas, Little Rock, Indianapolis, Buffalo, Cleveland, and Montreal.

Please don’t be confused when you hear about “percentages” of eclipse. Some people are lulled into believing that since they will experience a “90% eclipse” at their home, or even a “99% eclipse,” that there is no need to travel. This is a big mistake. Even with a 99% eclipse, the experience is completely different from a total eclipse. Unless you are paying attention, you might not even notice the 99% eclipse. But you’ll definitely notice the total eclipse just a few miles away, since it will become noticeably dark outside.

Also, in late 2023 or early 2024, you should order your eclipse glasses.

If you have kids who will be in school, plan on taking them out of school that day. Unfortunately, the 2017 eclipse showed that American schools had an irrational fear of the eclipse and actively prevented children from witnessing it. If you believe that your child’s school is more enlightened, then on the first day of the 2023-24 school year, you should have your children ask the science teacher if the school is planning a field trip to see it. If the teacher balks, then your children should let him or her know that they will be absent the day of the eclipse.

This is an entirely reasonable request for most schools. For example, students in Chicago could be placed on a school bus and taken to see the eclipse only a couple of hours’ drive away in Indiana. The expense will be less than other field trips taken to amusement parks, movies, etc. This is true for schools in many cities. They have the opportunity to let the kids witness an amazing scientific event, but only if they do some basic planning.

But I predict that this won’t happen, since most schools won’t think of the possibility until after it’s too late to make the necessary plans, or they’ll have the same irrational fears that showed up in 2017. It’s the duty of the students to pester the administration so that the necessary plans are made sufficiently in advance. And as I explained in 2017, if the school fails to act, then it’s reasonable for children to skip school on April 8, 2024.

Don Leary’s Record Store, Minneapolis, 1947

Shown here from 75 years ago are some views of Don Leary’s record store in Minneapolis. These images appeared originally in an issue of the store’s 12-page Don Leary Record News, which went out to over 25,000 people every month. The image was reprinted in the April 1947 issue of Radio Retailing., and that magazine highlighted the store’s ongoing advertising campaign, and the monthly newspaper was a key part of that advertising. The emphasis was on records bulletins and lists, but also highlighted the other aspects of the store’s business, namely, radio, appliances, and service.

The store had over a quarter million records in stock, and its business philosophy was that the logical place to buy a radio or phonograph was where you bought your records. It was good business, since the satisfied customer would keep coming back for records.

In addition to its own newspaper, Leary reported that the store was the largest user of newspaper advertising space of any record store in the region. He also made a point of having friendly relations with reporters, who came to quote him as the expert in all things involving records. For example, he had recently been quoted in the Minneapolis Star-Journal regarding juke boxes, which he viewed as a good thing for the welfare of city youngsters. (Incidentally, it was an industry in which he was also involved.)

More biographical information about Don Leary can be found at this link. The store was opened in 1941 at 56 East Hennepin Avenue, on Nicollet Island. That address doesn’t really exist any more, but would be at the spot indicated on the Google Maps image below:

Nicollet Island, 2022 (Google maps) and 1940.

The aerial view at the right was taken in 1940, and shows a business district along East Hennepin, the street connected to the mainland by the two bridges. Over the years, East Hennepin was paired up with First Avenue Northeast as complementary one-way streets. On the island, they form a short four-land divided road, and there are no lots directly adjoining it. To the North, there is now a view of De La Salle High School, and to the South, there is now a view of the Nicollet Island Inn, both of which would have been obscured by buildings on East Hennepin in the 1940’s. Leary’s store would have been one of the buildings on the South side of the street, probably the fourth one from the left.

I write about a lot of people on this site, and I think this is the first time I’ve written about someone who I personally met back in the day. I believe East Hennepin got its current configuration through the island in the early 1970’s, and Don Leary’s was long gone by the time I remember being there. However, from 1971 through 1979, he owned a record store in a small suburban strip mall at 2927 NE Pentagon Drive, St. Anthony, MN.

Despite the small size of that store, he probably still had a quarter of a million records in stock, of all genres. I was looking for something by Jimmie Rodgers, the Singing Brakeman (1897-1933). I asked Leary, who seemed to run the store as a one-man operation whether he had anything, and he asked me whether I actually meant the unrelated Jimmie F. Rogers, who was born the year the elder Rodgers died. When I let him know that it was the Singing Brakeman I was after, he commented something to the effect that he went way back, but showed me an assortment of his records.

Leary died in 2000 at the age of 92.

End of Civilian Radio Production: 1942

As we’ve previously reported, civilian radio production in the United States ended for the duration of the war on April 22, 1942. The graph above, which appeared on the cover of the April 1942 issue of Radio Retailing, showed how critical the radio repairman would be to keep the nation informed. As of that date, there were 57 million radios in American homes. In the years prior to the war, about 10 million new sets were made each year, but about 5 million old sets were scrapped by their owners each year, for a net increase of about 5 million.

With the end of production, the supply would remain at 57 million for the duration–but only if every radio was kept in service. If the prewar trend of 5 million radios per year being scrapped continued, then the number would be as shown in the graph at the right. And if repair parts became unavailable, then the situation would be even worse. The supply of radios would plummet, as shown by the steeply declining graph.

The message was clear: To keep the American public informed, dealers would need to concentrate their efforts on repairs, and manufacturers and the government would need to make sure that repair parts remained available.

1962 One Tube/One Transistor Broadcast Set

Sixty years ago this month, the April 1962 issue of Popular Electronics carried the plans for this hybrid one-tube/one-transistor receiver for the broadcast band. According to the magazine, the set would provide room-level volume on local broadcast stations, and while not hi-fi, was more listenable than one would expect from such a simple circuit.

The detector used a 12AE6-A tube as grid-leak detector. Since the tube was intended for hybrid car radios, it could run on a very low B+ voltage. In this case, that was 12 volts supplied by a filament transformer. The audio amplification was handled by a 2N231 germanium PNP transistor. The final semiconductor component was a 1N34 diode serving as rectifier.

The tuning coil was wound honeycomb style on a cardboard form. The set was said to pull in the local stations with an 8 foot antenna tucked behind a bookcase.

1950 Census

Image courtesy of Gerald Ford Presidential Library Facebook page.

Census data about individuals is private for 72 years. I assume that the thinking is that after 72 years, nobody really cares how much money you made or other details of your personal life. So after 72 years has elapsed, the information becomes public data.

Since census day was April 1, 1950, this means that the data for the 1950 census was made available on April 1, 2022. The census data for 1940 has been available online for ten years, and you can easily search it by many criteria, including name, at this link at Ancestry.com. (In fact, if you just Google the person’s name and “1940 census,” you’ll probably find the data that way. All of the original images of these records are available at the U.S. Archives website, but they cannot be searched by name on that site.

The images of the original 1950 records are now available at the U.S. Archives, which promises that the records can be searched by name. However, since most of the records are in cursive writing, the OCR process is not yet quite up to the task. However, it promises that the Artificial Intelligence is going to engage in machine learning. In particular, users are requested to transcribe entries, and I believe the thinking is that the AI is going to use these examples to learn the handwriting of individual enumerators, the people who went door to door writing down the data about the people at each house.

If you do try to search by name now, you’ll need to use a little creativity. In many cases, the last name is transcribed wrong, in which case you probably won’t find it. But if you search for just the first names in such a case, you might find the household, especially if you can narrow down the location well enough. But as the 1940 data proves, the searchability of the 1950 data is bound to get much better.

It took some searching, but I found my parents and grandparents. It was necessary, however, to know their address in 1950, at least approximately. Once you know where someone lives, you can find their “Enumeration District” with the interactive map at Ancestry.com.

Armed with this information, you can enter the Enumeration District, County, and State at the Archives.gov website.

You will then find a listing of all of the households in that neighborhood. Most of those listings seem to be about 25 pages long, and they are organized in the order in which the enumerator walked through the neighborhood knocking on doors. After you see which end they started on, it’s usually fairly easy to guess about which page the person of interest is on, and scroll through the pages to find them.

The example above is for then-Congressman Gerald R. Ford at his home in Washington, D.C. Since he was a member of Congress, the information for his household is struck out, with a notation that it will be transferred to his home district in Michigan.

The census contains the basic biographical data for everyone in the country. For about one person out of five, the enumerator was instructed to ask a few additional questions. My mother was one of those five people, and from her entry, I learned that in 1949, she earned a salary of $1600 per year working 41 weeks as a stenographer.

Prismatone Organ: 1947

This musician is playing the Prismatone electronic organ, what the April 1947 issue of Radio Craft asserted “promises to be by far the most attractive of all the lower-priced electronic music instruments.” The musician here was highly skilled, as the magazine noted that the instrument required a skilled operator.

The instrument consisted of a projector sending a beam of light through a translucent disc, which projected a rapidly altering pattern. The colors are solely for the benefit of the operator, as the instrument instead depended on the frequency of the pulsating light beam caused by the disc. The two wands contain photocells, and their output is the same frequency as the portion of the light at which they are aimed. Volume can be changed by altering the angle at which each wand was held. The outputs were fed into a high-fidelity audio amplifier.

The magazine noted that for an even more spectacular effect, the musician can wear finger rings with small selenium photocells in lieu of the wands.

The instrument was created by one Mr. Leslie Gould, a “well known Connecticut inventor of many electronic devices,” including “the Sonicator, a radar-like instrument for small boats.” One of Gould’s earlier inventions, part of a tuning mechanism, was at issue in Levy v. Gould, 87 F.2d 524 (C.C.P.A. 1937).

April 1957 Multiband Antenna

QST often contains cutting-edge technical articles, and the magazine’s April issue often contains the finest. It was no exception 65 years ago, and the April 1957 issue contained an article by prolific contributor Larson E. Rapp, WIOU, regarding the antenna shown above. Rapp noted that ferrite “loopstick” antennas worked well for AM radios, and surmised that they would make excellent multi-band transmitting antennas. He hoisted the model shown here atop his flagpole, and found that it performed exceptionally well.

But Rapp, being the technical genius that he was, carried the idea a step further. He noted that many antenna books depicted an antenna, along with its “image” directly underneath, below the ground. He surmised that if he buried the antenna, then the image would appear above the ground, without the need for any unsightly visible structure. He was able to get down to 35 feet, where he hit bedrock, and he buried the antenna there. He then hoisted a field strength meter up the flagpole, and sure enough, the maximum signal strength was achieved at 35 feet.

90 Year Old Radio Fan: 1922

In 1832, Andrew Jackson was re-elected President of the United States. It would be twelve years before Morse would demonstrate his electric telegraph between Baltimore and Washington. Slavery still existed in half of the United States, and would for more than thirty years. Abraham Lincoln wasn’t yet a lawyer, but held a bartending license and was about to make an unsuccessful bid for the Illinois General Assembly. Communications with other towns took days, if not weeks. In short, it was a long time ago. But people born that year would listen to the radio in their lifetime. But people born that year would listen to the radio in their lifetime.

But a lot was about to change. The news clipping above appeared in the Wilmington Daily Commercial.

Mrs. Sarah Frederick of Turtle Creek, Pennsylvania, was an avid radio listener. The paper noted that she was an avid listener to the radio chapel services from KDKA, and that she had recently celebrated her 90th birthday. She was totally blind but had frequently expressed her wonder and delight at this product of modern science.

And she was born in 1832.