"I enclose," writes Mr. Ross, "some prints of a 12-inch reflecting telescope I made with the help of your wonderful book 'Amateur Telescope Making.' About a year ago I picked up a volume of Flammarion's 'Popular Astronomy,' and after reading it determined to have a telescope and purchased a 4-1/2 inch Zeiss instrument with a triple lens objective. I then subscribed to the SCIEINTIFIC AMERICAN in order to get the monthly star maps. Thus I discovered you had a department devoted to this delightful hobby and got a copy of 'Amateur Telescope Making' at once. It proved to be a valuable treatise.

I made an 8-inch mirror first, to get some experience, and then tackled the 12-inch. It is remarkable how everything behaved just as the book explained, throughout the successive stages of grinding, polishing, and figuring the concave mirror. For grinding I rigged up a machine driven by a washing machine motor. This had a variable stroke, either straight or elliptical, and an adjustable feed for rotating the glass disks in opposite directions. It worked very well. [For the information of new readers, all the work is generally performed by hand.-Editor.] However, I did most of the polishing by hand. A true paraboloid showed up before the polishing was half completed. A hyperboloid next gave a little trouble, and later a central hill had to be removed before getting the mirror back to a true figure.

"The focal length is 110 inches. I get a range of magnification of from 66 to 458 diameters, using various eyepieces. The definition is good; in fact it compares very favorably with that of the Zeiss telescope, which is a high grade instrument. The mounting is a combination of alt-azimuth and equatorial, we live on the shore of Lake Michigan and the equatorial is not so convenient for sweeping around the horizon. I now have the Zeiss refractor mounted on the same equatorial head and the combination makes a good appearance.

"The observatory is 12 feet in diameter and is built over the edge of a bluff 86 feet above the lake. The inside rests on a concrete retaining wall, and the outside is supported on heavy steel columns."

DR. BERT R. CARLSON, dentist, 4100 East Lake Street, Minneapolis, Minnesota, sends in several photographs of an especially neat appearing telescope completed by him. "The patterns for the castings," he writes, "were made at home but I performed the machine work at the shop of a former employer. Everything is brass except the tube and the >e inch steel shafts. For the purpose I found that brass tubing was not stiff enough.

"The mounting without tripod weighs about 40 pounds and is none too heavy. It is intended for a column on a concrete base, which I hope will make it more steady. The declination and hour circles are part of the friction plates. The slow-motion member holds the vernier.

"I enjoyed the polishing. My first pitch lap was too soft and by the time I had learned to interpret the shadows in the shadow test the speculum was deeply hyperbolized, with a hole in the center that could be seen before the knife-edge cut off the light. It required seven hours and two pitch laps to bring it back to a sphere, but I learned a lot about shadows, strokes, and so on, in doing it. I believe it is better not to get a parabola by beginner's luck the first time, but to have to work for it. The instruction one thus gets is worth the effort.

"The mirror has a focal length of 53 inches and the entire instrument cost less than 50 dollars."

THE Fourth Annual Convention ("get-together") of amateur telescope enthusiasts will be held Saturday, August tenth, at Stellafane, near Springfield Vermont. Postcard invitations will no doubt be sent to amateurs in nearby states, but it is emphasized that all are welcome. You need no invitation, and if you should happen by some omission not to receive one, come anyway. These gatherings are for the main purpose of permitting amateurs to meet one another trade ideas and experiences, and talk.

IN last month's issue we spoke of the possibilities of making an amateur hobby of seismology. No returns have yet been received as this is written, because that issue of the magazine is not quite yet before the readers. However, there is still another hobby which a number of our readers have suggested for popularization-amateur microscopy. It would not pay to make one's own microscope (although this might prove interesting if the practical instructions were available) because the market is nowadays full of suitable microscopes at a cost of only about 20 dollars.

Microscopy is a large subject, a "large order," too, for any editor who might rashly attempt to pose as an authority on it. Even one single aspect of it into which the present writer has slightly looked, that is, the study of the microscopic living forms of life in pond water, ditches and streams, is too broad a subject for any but a whole-time specialist to encompass.

However, this one phase of microscopy affords a most fascinating field for the scientifically inclined amateur.

Few people realize the immense number of interesting live forms of microscopic life to be found in half a drop of pond water. One can remain for hours watching the antics of an amoeba, or the beautiful rotational motion (which is really an optical illusion) of a rotifer. One other form, less animated, the diatom, is the subject of an article in the present issue, and the reader's attention is called to the footnote placed beneath that article (page 113). These and hundreds, yes thousands, of other forms are widespread in their distribution; in fact they vary little throughout the world, because they are so easily transported by natural agencies. You will find them in the average ditch; in the river, creek, and brook; in the old swimmin' hole; and doubtless in the tap water in your kitchen.

A microscope which magnifies more than 100 diameters will suffice very nicely to render them visible, and a few old bottles and inexpensive gadgets complete the outfit. How many readers are sufficiently interested in this outdoor hobby for the amateur scientist to write in and say so?-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.