"I feel almost certain that there are dozens of amateurs who could take a lot of pleasure in making a solar spectroscope and watching solar prominences. I do not think there are many amateur astronomers and telescope makers who would not become intensely interested if they saw some of the objects I have seen on the Sun. It is quite common to see great masses of gas shoot up 75,000 or 100,000 miles high, then die away to nothing in a few hours. The forms they take are varied and graceful, in fact no two are ever just alike. Sometimes they are like spikes, again they resemble jets or plumes, or a basket of flowers, and sometimes they look just like ordinary clouds. The latter are termed quiescent prominences, and often look somewhat the same for a long time.

"My experience with small star spectroscopes quite confirms your statement that they are not satisfactory on small telescopes. I do not get very good results even using my 12-inch reflector. I can see only a few lines in bright stars, but even that is of some interest. I did not know whetherthe replica grating would work well for solar work or not until I tried it, but I ordered one and have been using it about a year, and it works.

"I am now trying to find out where I can get a larger one and a few more hints on spectroscope construction before I start on a Hale spectrohelioscope."

Since Mr. Dunlop sent us the above letter, Dr. Hale's description of the spectrohelioscope has appeared in the new edition of the SCIENTIFIC AMEPLICAN book "Amateur Telescope Making," and Mr. Dunlop advises us that he expects to convert his equipment into a spectrohelioscope, using the blueprints mentioned in the book and housing the apparatus in the structure shown in the illustration. All the solar activity he describes, and more, can be observed to far better advantage with the new apparatus which can be made at moderate cost.

Harold A. Lower, 1032 Pennsylvania St., San Diego, California, made a telescope which he has used successfully for lunar photography. Mr. Lower writes:

"My telescope was made from the instructions in 'Amateur Telescope Making.' The making of the mirror is so well covered in the book that comment on it is unnecessary. The mount is the German equatorial type and is made from the front hub assembly of an old auto. The only thing needed to adapt it to its new use was to remove the steering spindle bushings and replace them with solid plugs, which were then bored at right angles to the wheel spindle. The wheel spindle forms the polar axis, and as it is mounted on ball bearings it moves very smoothly and easily.

"The telescope tube was made of wood. as in this location the mirror and prism do not fog as quickly in a wooden tube as in one of metal. There is usually a very heavy dew fall here in San Diego, and the wooden tube enables one to use the telescope when an instrument with a metal tube would be almost useless."The setting circles are made from printed paper disks which were purchased for 20 cents each, from a dealer in engineering supplies. They answer the purpose very well.

"The box over the eyepiece is used only for photography, and is easily removed when the telescope is used for visual work.

"I will be glad to get in touch with anyone else who is interested along the same Iines that I am."

When the Editor expressed a desire to publish more details about the use of the telescope for lunar photography, Mr. Lower furnished the following statement:

"I have found that it is easy to photograph the Moon with a home-made telescope. A box, open at both ends, is mounted on the telescope over-the eyepiece, to hold a plate holder or a ground glass for focusing. An eyepiece of about one-inch focal length is used, partly to magnify the image, and partly because it is more convenient to focus with the eyepiece than to adjust the plate at the focus of the mirror. One should not have the plate more than three or four inches from the eyepiece, as a large image will require too long an exposure.

"I use Eastman cut film, Super Speed, instead of a glass plate, as it is very fast and does not show a halo around a bright object, as do ordinary glass plates. -The cut film is placed in a sheet metal adapter and loaded in a plate holder just like a glass plate.

"No shutter is required. A sheet of cardboard is placed over the front of the telescope after the image of the Moon has been focused as sharply as possible on the ground glass. Then a film holder is substituted for the ground glass, the slide is removed, and the exposure made by removing the cardboard from in front of the telescope and replacing it as quickly as possible.

"As Super Speed film is very sensitive, the exposure needed is only about a fifth of a second, which is fast enough to prevent the telescope is not equipped with clock drive.

"The enclosed pictures of the Moon were made with a six inch mirror and an eyepiece of about ) inch focal length. I believe I can make better ones, but these will give a fair idea of what one can do with a six-inch mirror." (One of these is reproduced in "Amateur Telescope Making."-Ed).

"An ordinary negative eyepiece works all right, but an achromatic eyepiece would probably be better with high magnification. "

J. M. de Jager, Embong Kenongo 33, Soerabaia, Java, Dutch East Indies, sent us rather long ago a photograph showing progress on a six-inch mirror. It is a long way from America to Java but we have records of amateurs making telescopes in many other distant lands and we here urge them to send us photographs and descriptions of their telescopes. Says Mr. de Jager:

"In my last letter to you I promised to write to you about my progress while making the mirror of my future telescope. As I have only a little spare time, I progress very slowly. I send you the photograph. You can see that I am working temporarily in the open air."-A. G. I., Tel. 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.