Approved by Over 200 Experts New Crosley Engineering Achievement THREE tube set with five tube efficiency It was only after a year of constant experimenting, "Tried one of these sets out and obtained wonderful IS All Crosley Regenerative Sets U. S. Patent No. 1,113,149 This new Crosley triumph is called the Trirdyn because The Crosley Trirdyn in range, volume and selectivity antenna. The opinions of many experts have convinced us that Practically every radio dealer can furnish you Crosley SEE THIS NEW WONDER AT YOUR DEALERS THE CROSLEY RADIO CORPORATION POWEL CROSLEY, JR., President Formerly The Precision Equipment Company and Crosley Manufacturing Company 717 Alfred Street, Cincinnati, Ohio 2 Buhr A House of Wonders in which Science is the host has just opened Mars comes its closest to us on August 22, reviving keen interest Are you afraid of lightning? You need not be, once you under- That costly error-how did it happen? There it is, yet you are And more than 200 other fascinating articles and pictures In the new House of Won- In This Issue Desert Cliffs Yield Ancient Secrets.. The World's Greatest Spectacle. What to Do with a Good Idea.... Masterpieces of Insect Architects. Pencil and Vanity Case Combined. New Motor Fuel Silences Knocks. Better Tools for the Housewife. Weighted Ash-Tray Won't Spill.. Telescope and Microscope in One. PROTECTION FOR YOU By COLLINS P. BLISS, M.A. Popular Science Institute of Standards HE newly established Popular Science worthy and impartial guidance in your purchases of radio equipment, tools and other articles of a technical or semi-technical nature. As an important part of its service the Institute guarantees to you the reliability of every radio product advertised in Popular Science Monthly. Engineers of the Institute protect you thoroughly by exhaustive tests which for radio sets consider: 1. The external appearance 2. Workmanship 3. Sensitivity 4. Selectivity 5. Amount of amplification 6. Wave-length range 7. Quality of reproduction When we first receive a set for test in our laboratories we examine it to determine that it meets the requirements of the average user. Each piece of apparatus is inspected to determine that it is constructed properly mechanically, and is built substantially; that all soldering is perfectly done and that it will give the maximum electrical efficiency. Then laboratory tests are made. Sensitivity is determined by means of an oscillator or a miniature transmitter, which has been adjusted previously for a predetermined output, and then started and placed so that the antennae coils of the receiving and transmitting sets are in a coupling position. The signal strength at the end of the detector tube is measured. By varying the transmitter output of the oscillator we can imitate the actual conditions found with stations broadcasting at different power outputs. By vary IN YOUR RADIO PURCHASES ing the coupling we can approximate the N TEXT is a test for selectivity. With the same set-up as in determining sensitivity, we can tune in on the oscillator which has been started with a predetermined coupling and transmitter output. The signal current is measured on the detector. Then the transmitter is detuned until the signal current is reduced to about one-half. By use of formulas, selectivity of the set is determined in terms of the frequency change. Thus the less the change is required in detuning the transmitter, the more selective is the set. IS POPULAR SCIENCE Monthly The above seal on an advertisement indicates that the products referred to have been approved after test by the Popular Science Institute of Standards. Popular Science Monthly guaran. tees every article of merchandise advertised in its columns. Readers who buy products advertised in Popular Science Monthly may expect that these products will give absolute satisfaction under normal and proper use. Our readers in buying these products are guaranteed this satisfaction by Popular Science Monthly. THE PUBLISHERS. The amount of amplification is determined by using the same set-up but with modulated audio-frequency. The amount of amplification is measured by comparing the signal strength with the amplifier and the signal strength using the detector tube only. In this way we can determine whether or not a set gives a sufficient amount of amplification. After this a test of wave-length range is made. A measure of the range of the set as a receiver, its maximum and minimum range of wave length, is made. To be an efficient receiver, it must, of course, be able to cover the usual wave lengths used by the different broadcasting stations. The quality of reproduction is another important factor. The set is operated under average conditions and a determination of the quality of reproduction is made. The final test of the series is that of operating characteristics. A determination of the ease of tuning is made. Then, too, there must be a sufficient independence of tuning. It must be possible to tune in accurately; for this you require fine control. Finally, the set must remain put after it is adjusted. RADIO set must pass the rigid tests A outlined above, to receive the Popular Science Institute of Standards approval. Readers are urged to make full use of the service of the Popular Science Institute of Standards, as through the careful testing of a staff of competent engineers the Popular Science Institute of Standards assures every reader that the Radio Products displayed in our columns are of good value and will under normal and proper use give absolute satisfaction. Test of radio apparatus is only one of the functions of the Popular Science Institute of Standards. In the next issue of Popular Science Monthly we will tell how we protect you in your purchases of tools. P Radio's Part in in Politics RESIDENTIAL campaign year 1924 brings with it a brand-new puzzle for the politician. The puzzle is the radio fan. Politics is largely a matter of publicity. Since the 1920 campaign, radio broadcasting has developed into one of the greatest mediums of publicity in the land. Hence the politician's concern. When those fellow Ohio editors-and publicity experts-Warren G. Harding and James M. Cox ran against each other for the presidency, there were but 15,000 sets in the country. That figure is the estimate of the Department of Commerce radio experts. Today, Secretary Hoover estimates that there are no less than 5,000,000 radio receiving sets in regular use. Since through loudspeakers and extra head sets-each receiver probably averages at least two listeners, it is probable that some 10,000,000 people hear what the radio waves are carrying each day. To a political spellbinder, eager to sell By Edward G. Lowry Mr. Lowry is one of America's fore- his wares, that is an audience such as no man before, even in his wildest dreams, ever hoped to reach. Probably the most ambitious spellbinder this country has ever known is James M. Cox. His campaign in 1920 was a marvel to foe and friend alike. During the last three months of his campaign, Cox traveled more than 10,000 miles in his special car, talking on an average of 10 times daily to audiences ranging from mere handfuls of people to the 30,000 who assembled to hear him on notification day at the Dayton Fair Gounds. Cox was able to achieve this almost superhuman task because he was physically stronger than nine out of 10 men of his age; and he was considerably younger than the average presidential campaigner. Also, to keep himself fit, he carried with him his own cook and masseur. HOR OW many people heard Mr. Cox? There is no way to ascertain the exact number, but newspaper correspondents who traveled with him once figured that he may have made his voice heard to 1,500,000 at the most. A more conservative estimate would be 1,000,000, or but one-tenth the number the Democratic candidate in 1924 can reach in one evening from his comfortable front porch, if he can arrange for an adequate chain of broadcasting stations to carry his message to the radio fans of the whole country. Indeed, through the magic of radio, either of this year's candidates, if his line is connected with such a chain of |