"The average man may know in a vague general way that much of the astronomer's knowledge of the stars comes by way of the spectroscope, but the black and white spectrum as they are generally known, mean little to him. The accompanying photograph is the result of trying to bring these spectrum lines to him in color and action. By means of this instrument, which I have called the 'spectra demonstrator,' one can see and compare the spectra of a number of gases and metals- a veritable picture show in colors-and it will help the amateur or student to realize that when the astronomer with his telescope sees these same lines and colors in a star he knows that the star contains the particular gas or metal that they have been looking at in this instrument.

"Then, if we tell him further that the broad spectrum lines of one gas show the movement of gas in molecules, while the narrow spectrum lines in the adjoining tube which he sees at the same time, show the result of the knocking off of electrons from the gas atoms, he will not only obtain a beautiful sight-for the colors are wonderful-but he will begin to get some idea of electrons, atoms, and molecules, and their action in matter. This sort of a 'moving-picture show' interests and fascinates not only the man who knows little of physics and astronomy, but the student also."The instrument is complete, self-contained, is suited for both individual as well as class room use, and is operated by plugging in on the ordinary house light current. It contains eight vacuum tubes filled with gases, such as oxygen, hydrogen, helium, mercury, and so on; a holder for an open arc, to show spectra of metals such as iron, copper, salts, and so on; one 4000-volt transformer and one 10,000-volt condenser, both properly insulated for safety; and one direct-vision hand spectroscope, with wavelength scale and device to show spectra of two gases at the same time, so that the lines and colors may be comparedand examined in detail.

The base box is 12 inches square, six inches high. On it is placed a revolving frame carrying the vacuum tubes. The spectroscope is held stationary in a socket in the base box, while the tubes revolve; thus giving a succession of spectra so they can be easily examined and compared.

"The instrument will be put up in a complete unit-a precision laboratory apparatus. It will be built by the same firm which is building the Hale amateur spectrohelioscope. The vacuum tubes may be purchased separately.

"The instrument has been seen and examined by some of the officials of both Mt. Wilson Observatory and California Institute of Technology and has received their warm approval. While it is not a cheap affair it may be duplicated in an inexpensive and simple form by the amateur, using a Ford coil for a transformer and a condenser made from less than a dollar's worth of tinfoil and glass; the spectrohelioscope may be home-made, using a replica grating in place of prisms.

"In this shape the instrument is interesting and educational. It is perhaps my most valuable contribution to the advancement of the cause you are fostering. It is for the free use of the public."

R. D. Cooke Box 41, Nameoki, Illinois believes in a clock drive and has made a simple but practicable one. He writes: "I am sending you some pictures of an eight-inch telescope with a clock drive, which may be of interest to some of your readers I am extremely pleased with the way it works.

"The driving clock is the movement of a dollar-and-a-half alarm clock and serves merely to control the speed. The main source of power is the weight operating over a sprocket on the worm shaft. The large gear floats on the center pin and turns continuously. The casting carrying the hour circle rests on the edge of the gear and is carried along with it, except that it may be moved by hand to any position desired. As soon as the hand releases it, the clock begins to carry it along.

"Since making the pictures I have mounted a flashlight bulb under the reading glass for illuminating the declination circle.

"To show the accuracy of the mechanism I sighted on the nebula in Orion, and then went into the house for nearly an hour. Going out again I found the nebula exactly centered in the field. I am tempted to try some photography with the telescope and would be glad to hear from anyone who has done any work of this kind."

Martin G. Murray, a post office clerk at Huntington Beach, California, writes: "As soon as 'Amateur Telescope Making' was off the press, I purchased a copy. However it was not till the latter part of 1927 that I had the opportunity to begin work on my telescope. I am especially interested in the study of sunspots, and have just made an attachment that makes it possible to chart the spots. I am well pleased with the entire instrument and am very grateful for all help received through the SCIENTIFIC AMEBICAN. I am enclosing a photograph."

The Telescope Editor has just returned from an excursion in Europe, which included visits to several places of astronomical, and particularly telescope making, interest. Several large optical shops in Great Britain and Germany were visited. No real T.N. should leave London without making a sacred pilgrimage to Burlington House to see Newton'soriginal reflector with its tiny mirror; nor fail to go to Florence where, at the Museum of Physics and Natural History, he may approach within close view of Galileo's famous original telescopes.

-A. G. I., Te1. Ed.

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.