Agricultural Chemistry, J. F. Lyman; Agricultural Engineering, F. W. Ives; Agronomy, A. G. McCall; Anatomy, F. L. Landacre; Botany, J. H. Schaffner; Ceramic Engineering, Carl B. Harrop; Chemistry, Jas. R. Withrow; Civil Engineering, F. H. Eno; Forestry, N. W. Scherer; Geology, C. S. Prosser; Horticulture, V. H. Davis; Industrial Arts, W. A. Knight; Mathematics, C. J. West; Mechanical Engineering, Horace Judd; Pathology, Jonathan Forman; Physics, F. C. Blake; Physiology (General) R. J. Seymour; Physiology (Medical), Clayton McPeek; Public Health and Sanitation, E. R. Hayhurst; Zoology and Entomology, J. S. Hine.

The Ohio Journal of Science is to be considered as a continuation of The Ohio Naturalist. It is hoped that with the wider field covered, it may interest a much larger number of the scientific people of the state, and be financially supported so that it may soon develop into a journal of high standard. It is the intention of the present Editors, with the large field before them, to publish results of research as well as articles of general interest in the advancement of Science. On the natural history side the aim at present will be to pay more especial attention to the biology, geology and geography of Ohio, but articles dealing with any other region will be acceptable.

THE MAKING OF A PHOTOGRAPHIC OBJECTIVE.

Being a Description of a Course in Applied Optics Offered at the
Emerson McMillin Observatory of the Ohio State University.

H. C. Lord.

Photography, in its more serious phase, has taken an important place in almost every field of human activity while in its lighter mood, through the development of the “Kodak” and the roll film, is giving us one of our most delightful pastimes. As a condition for the best work, a high grade lens is a necessity and especially so for those extremely short exposures required in the photography of rapidly moving objects. It often happens that some of the most perfect and at the same time most difficult specimens of optical design are found on cameras so small that they can be easily carried in one’s coat pocket. These so called anastigmats furnish to the optician a difficult and yet at the same time most fascinating problem for mathematical investigation. Thousands of photographic objectives are placed on the market every year, yet though almost every branch of engineering is covered by our technical schools, I know of no place outside of Germany where a student can be instructed in the design and construction of a simple photographic objective. Professor Silvanus P. Thompson in his inaugural address as President of the British Optical Convention held in London in 1912, states: “In the Universities and Colleges the only people who are learning Optics are merely taking it as a part of Physics for the sake of passing an examination for a degree, and care nothing for the application of Optics in the industries. They are being taught Optics by men who are not opticians, who never ground a lens or calculated even an achromatic doublet, who never worked an opthalmoscope or measured a cylindrical lens.” Further on he speaks as follows: “What is wanted is an establishment where the whole atmosphere is one of optical interest; where theory and practice go hand in hand; where the mathematician will himself grind lenses and measure their performance on the test bench; where braincraft will be married to handcraft; where precision, whether in computation or workmanship, will be the dominating ambition.”

Some four years before the above quotations were written, the author started to work up a course in Optics which should aim, not only to give to the student a knowledge of the fundamental theory of lenses, but should also apply those principles to the methods of optical design and thus enable him to compute the curves of the component lenses of a photographic objective. This has now been fairly well worked out and is given in the Arts college under the official titles “Astronomy, 107, 108, 109 and 110.” The basis of this course is “A System of Applied Optics,” by H. Dennis Taylor, the inventor of the Cooke lens. This splendid volume develops, from the standpoint of geometric optics, a complete discussion of the formation of an image by a combination of any number of lenses, but does not apply the methods and formulae there developed to the actual design of a photographic objective. The writer of this paper was, therefore, compelled to work out this part of the theory for himself and, as he had always felt that all mathematics should ultimately end in arithmetic and that all arithmetic should ultimately end in doing something, he resolved at the outset that the course should end in laboratory work in the actual computation, grinding and polishing of lenses. As to how well this has succeeded, I will let the illustrations which accompany this article speak for themselves. Suffice it to say that the half tone cuts were made from five by seven enlargements from negatives, one and three quarters by two and one-eighth inches, taken with a lens designed and built at this observatory and working at an aperture of F six. A peculiar feature of this lens is that it is composed of four lenses all cut from the same piece of crown glass. This lens beautifully illustrates the importance of adding to the theoretical side of the course, the practical work in the laboratory in construction and testing as this lens, though in the main satisfactory, has one serious defect and a defect which is very instructive in that it shows that at a certain point in the design, the theory was weak and needed to be extended and enlarged. It should be stated that this theoretical investigation is now completed and ready to be put to the test of practice.