"The readers of the 'Back Yard' may be interested in the accompanying photograph and description of my reflecting telescope, made according to the directions in the excellent SCIENTIFIC AMERICAN handbook, 'Amateur Telescope Making.'

"I obtained my glass disks and abrasives from John M. Pierce of Springfield, Vermont, and in this way got just what I needed in the shortest time and with no bother at all. Making the mirror occupied my evenings for about three weeks. As a post on which to mount the tool I used a heavy chest with the handles removed. The chest was placed on end on the cellar floor and loaded with a big chunk of concrete. This formed a very rigid support of smaller dimensions than the barrel usually recommended for this purpose. Also, it brought the tool to just the right height from the floor for convenient working, which seems to me to be an important point.

"Every stage of mirror making is interesting, but the testing by Foucault's method is particularly fascinating, and gives one a new insight into the accuracy of physical measurements, without the use of any of the complicated costly laboratory instruments.

"The mounting was made almost entirely of wood, which is comparatively heap and can be worked with only a small number of hand tools. The tube was made of one-half Inch white pine, six and one half inches square inside. The bottom of the tube was made of two pieces with the grain crossed. This forms the cell for the mirror. The diagonal is a one-inch prism carried in a tin support, and this with the adapter tube is removable as a unit, since both are carried by a block of hard wood which is attached to the telescope tube by bolts and wing nuts. The holes in the block are somewhat large, so that a certain amount of adjustment can be made in lining up the mirror, prism, and eyepiece.

"The telescope is carried by an equatorial mounting made by assembling small pieces of one- by four-inch maple. The mounting is very solid, being put together with countersunk screws and glue. The axes are one-half inch lag bolts with washers and wing nuts. The use of this type of built-up mounting avoids the necessity of buying any large blocks of hard wood which are more difficult to work. The axes are well greased and the motion is smooth.

"The setting circles are made from four five-inch metal protractors such as are used in drafting work. The cross-bars were cut out and the graduated arcs soldered to circular pieces of tin. These circles answer very well for rough work.

"The mirror was silvered by Brashear's process, and strangely enough this proved to be one of the most difficult parts of the entire job. However, the technique was finally mastered and a good heavy coat of silver obtained on the face of the mirror.

"The total cost of the telescope was not far over 25 dollars, and the performance, for a first attempt, exceeds my expectations. The light grasp is astonishing to one accustomed to very small refractors, and the complete absence of chromatic aberration is a great advantage. The picture which even this little instrument gives of the magnificent Orion nebula with the beautiful little stars of Theta Orionis nestled in the midst of the silvery haze will not be soon forgotten by anyone unacquainted with the wonders of the heavens."

Mr. Boutell comments on the height of the post used during grinding and polishing. Many amateurs use too low a post, and thus they acquire an advanced ease of the "wash-tub bends." For comfort the top of the mirror should come about on a level with one's floating ribs. It is also possible to sit down at the work.

A. R. Clish, 71 Winter St., Portland, Maine, sends in a photograph of a simple refractor he recently assembled. Although he makes no mention of a crown and flint lens for the objective or of the rather exacting calculations involved in designing such a lens, he states that his telescope functions well enough to gratify him. This is what he writes:

"For the past two years you have published a each month the description of a home-made telescope. Most of these descriptions have mentioned the long time necessary to grind and polish the mirror. I am a student at a normal school, having neither time nor facilities to make such instruments. I set out to design a telescope simple enough for my troop of Boy Scouts to use when they wished.

"I asked a local optician to make a lens for me. I suggested that he do it in his spare time, and that it would be an experiment on his part to see if he had the ability to do it. He made me a very good lens three inches in diameter, having a focal length of 24 inches. The lenses for the ocular had me stumped for a time but I happened to think of the lenses in the finder of a camera. I got three of them from a camera repair man for only 15 cents.

"I had a ring of brass made to hold the objective. Quarter-inch brass works nicely. This was attached by means of a right angle of brass to the heavy (one by two inch) wooden beam of oak.

"The eyepiece tube was made of a piece of one-half inch pipe and a cap to fit, both of brass. A four-inch piece of pipe is long enough. A hole is drilled in the center of the cap, to finish the eyepiece. The lenses are put in the cap, one on top of another, and pieces of sealing wax hold them in very well."

Mr. Clish next describes his mounting, details of which are, however, made sufficiently clear in the photograph. The eyepiece is attached to a piece of wood which slides on the main bar, and is held in place by means of two metal guides.

"The tripod," Mr. Clish continues, "is easily made from stock one and one-fourth by three-fourths of an inch. My instrument magnifies about 30 diameters. I can use four of Jupiter's satellites. The mountains on the Moon show up very well I can count about 60 stars in the Seven Sisters. I am certainly glad that I built the telescope. It has given me much pleasure."

-A. G. I. Tel Ed.

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