"I send prints of a reflector which I have recently completed. The mirror is six inches in diameter with a 48-inch focal length. One of the outstanding features of this design is that the tube with all of the optical parts can be removed from the yoke in a few minutes and taken indoors for protection. This I find is a great convenience as I have no housing, and one feels much better with this part of the telescope indoors.

"The yoke and base are made of one and three-quarters by three-inch birch, glued and screwed together, and the whole is covered with spar varnish. This construction is very strong. However, it is not so heavy that it can not easily be moved from place to place if necessary, and with a little care in placing, I find it to be very steady.

"I think the most interesting part of this work, other than the star gazing, is making the mirror. This, although tedious, is interesting from the very start, and one soon loses all of the fear he ever had about working glass. Even the testing with the knife-edge, while trying upon the eyes, has its great reward when the telescope finally is tried on the Moon or stars. I expect to essay a 10- or 12-inch mirror soon."

With this issue we at last announce the publication of a second and revised edition of the SClENTIF1C AMERICAN instruction book "Amateur Telescope Making." The word "revised" is, however, much too mild for the book has been considerably more than doubled in length, now consisting of 286 pages, instead of 102 as formerly. Virtually all of the matter contained in the first edition has been retained, and thus the beginner may continue to use the book as before-to instruct in making a satisfactory telescope capable of magnifying 50 to 200 diameters without expending more than 25 or 35 dollars for the entire job.

To the elementary instructions by Porter, Ellison, Ions, Pierce and others, much new matter, some of it more advanced, has now been added. Porter adds eight new chapters: a chapter of "wrinkles;" a chapter telling how to adjust the telescope and put it into alignment with the co-ordinates of the heavens; a chapter explaining how a telescope having setting circles is used to find the otherwise undiscoverable show-pieces of the skies; one describing a number of ways to bring the observer indoors away from the cold of winter and the mosquitoes of summer, yet use the telescope to almost equal advantage; practical instructions for making a prism or diagonal; a chapter telling how to make an optical flat or plane surfaced mirror; one on making the Cassegrainian type of telescope, and one which gives complete and detailed instructions for designing and making both the lenses and the metal parts of an eyepiece of high quality and appearance. The instructions for making a flat and a Cassegrainian telescope are virtually unique; they have never been in print anywhere before, in satisfactory detail.

Professor Charles S. Hastings of Yale, who for years designed the curves of the famous Brashear telescopes, contributes to the new volume two chapters on eyepieces, giving the amateur a full insight into the many optical principles involved in eyepiece design, selection and use.

Ellison's treatise on the objective lens has been included in the new edition. This is the first time we have emphasized the refractor as a suitable outlet for the mechanical instincts of the advanced amateur. There has been a small but steady demand, during the past two years, for these instructions and we therefore obtained from the Rev. Mr. Ellison a complete revision of the theoretical part of his original treatise on the objective lens. No treatment of the subject even approach that by Ellison in length and usefulness

Silvering has been a stumbling block for the average amateur, and we confess that the instructions contained in the first edition of "Amateur Telescope Making" were not sufficiently well rounded to obviate certain mistakes. The section o silvering has therefore been expanded by the addition of six new pages.

Many advanced amateurs wish to construct machines for grinding and polishing their mirrors. Hand work is equally good although more laborious. The new edition contains a thoroughly illustrated section on machines, describing those used by several workers, and reprinting, with the original illustrations, the description by Ritchey of the type of machine he uses for all his work.

A. W. Everest contributes a complete, practical, illustrated section, telling exactly how to use the new H.C.F. (honey-comb foundation) lap which he discovered. The use of this lap cuts down the time of polishing a six-inch mirror from six hours to two.

Amateurs who want to take up something really lively will be delighted with Dr. George Ellery Hale's 22-page instructions for making the new spectrohelioscope, a remarkable instrument which will enable them to sit in their garage or other building and actually watch the motion of those vast red prominences on the Sun which often rise 100,000 miles above its surface within, the space of a few minutes. The apparatus is remarkably simple and lies within the means and capabilities of the amateur. We amateurs are indeed fortunate to have enlisted the interest and support of so famed an astronomer as Dr. Hale of Mt. Wilson Observatory. -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.