"I have been interested in astronomy and telescope making for many years," he writes. "My early attempts at the latter were amusing but instructive failures. All this was changed, however, when I happened to see Richey's papers in the SClENTIFIC ARERICAN Supplement which made it easy to prepare proper abrasives and tools, and I determined to make an eight-inch telescope at the earliest opportunity. I made a machine somewhat along the model of Richey's but using belts instead of gears.

"The cutting of the disks was done on the machine. The first tool I used was cast iron, used as it came from the mold but dressed down with a file as the grinding showed what its proper shape should be. My first mirror failed to show any considerable lights and shadows on the Foucault test, which caused me to think that there must be something wrong with the test; however, upon trying it on the moon, it behaved so well that I decided to mount it and use it.

"I then decided to try to make a better mirror and, using a glass tool and other improved methods, expected to exceed my first attempt easily, but was somewhat surprised to find that I couldn't even equal it until after many months of work.

"Having succeeded in my eight-inch, I decided upon a very ambitious program of making a 15-inch, with building, dome, proper mounting, clock drive, push-button slow motions, setting circles, and other accessories Upon this work I have been engaged in my spare time since about 1913.

"The electric drive is a slow-speed motor controlled in this way: A Watt's governor retards the position of the commutator if the speed is too high or advances it if the speed is too low, thus maintaining a constant rate of speed. It is entirely successful, the cost was much less than the gears in the usual clock drive, and it never needs to be wound up.

"All my work would doubtless have been made easier and shorter if 'Amateur Telescope Making,' the SCIENTIFIC AMERICAN instruction book, had been published sooner."

HOW well professional and amateur astronomers co-operate is illustrated 1t by an incident involving Dr. Robert S. Richardson of Mount Wilson Observatory, acting in the capacity of Sherlock Homes, and Mr. A. R. Dunlop, R.R.2, New Westminster, B. C.

Mr. Dunlop had sent the Telescope Editor the following communication:

"I am sending a photo of a pencil sketch of a prominence as I saw it with my spectroscope. It represents the change which took place in one half hour, August 19,1927.

"I would advise all amateurs who can do so to construct the Hale spectrohelioscope but I also feel that there are dozens who could easily make a simple spectroscope but who could not afford a grating for spectrohelioscope. It is to these amateurs that I would like to deliver a little message, as the results on prominences with a spectroscope costing not more than 10 or 15 dollars to make, are quite surprising.

"I am using the polar heliostat form of mounting as shown on page 50, Number 4, of 'Amateur Telescope Making,' but a spectroscope could be used with any equatorially mounted telescope. The Springfield or Pasadena mountings are especially suited to the job, owing to the fixed eyepiece. A four-inch reflector is just the thing for this purpose, and it is quite large enough. A long-focus telescope is not so good, as only a small portion of a prominence can be seen at once with a large image on the slit."

It was suggested to Mr. Dunlop that he send prints of the same photograph of his drawing of a solar prominence to Dr. Richardson, who specializes in solar research at Mount Wilson Observatory. Dr. Richardson immediately went to the files of plates at the Observatory and located photographs of Mr. Dunlop's prominence. His letter to Dunlop is as follows: "I was very glad to examine your excellent drawing. It enabled me at once to identify the prominence on our plates. There were several photographs of this prominence and also an Ha spectroheliogram of the spot in which the prominence originated. I enclose some enlargements of both.

"A special series of observations had been made on this object, but we had quit at 2 P.M. Your drawings indicate that you observed the prominence shortly before it 'blew up.'

"Prominences of the eruptive type are frequently accompanied by magnetic storms. Our magnetometer records show a violent storm lasting from August 18 to 21, which was probably caused by this spot.

"I should think that very valuable work could be done with small equipment in studying eruptive prominenees. Investigation of the relation between magnetic storms and eruptive prominences requires nearly continuous observation, and hence important contributions might be made by amateur astronomers, supplementing the work of large observatories.

"Observation of prominences in different lines of the spectrum is also of interest. The hydrogen lines, of course, are always bright, as well as the D3 line of helium and the H and K lines of calcium."

MR. W. G. HALE, of the University of Washington Library, Seattle wishes to borrow a telescope or a mirror for use in connection with astronomy talks he is giving to boys. Volunteers are requested to communicate with Mr. Hale direct-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.