PHYSICAL LABORATORY REPORT.

The annual report of the Jefferson Physical Laboratory for 1899-1900, presented by Professor John Trowbridge, is printed in the President's Report. It contains in addition to the usual routine work of the department, the results of a large amount of experimental research, which has been carried on during the past year, by Professor Hall, Sabine, Peirce and Trowbridge. Many of these experiments are important, not only because of their scientific value, but also because of conclusions drawn from them which will have an important bearing on subjects, both of medical and astronomical interest.

One of the most important of these is in regard to the question of the nature of the atmosphere of the sun. The experiment was performed by Professor Trowbridge and consisted in a careful study of the effect of powerful discharges of electricity on the spectra of various gases. Although great care was taken in drying and pur fying these gases, it was found that hydrogen, nitrogen and rarefied air gave substantially the same spectrum under the same conditions and as a result of the powerful electrical discharges the aqueous vapor was released from the walls of the spectrum tubes. From this investigation it was concluded that oxygen does exist in the atmosphere of the sun. It was also found by a similar study of aqueous vapor in the X-ray phenomenon that, probably by varying the conditions of the strength of the electrical discharges and the condition of the vapor, X ray photographs can be secured of tendons and muscles of the human body, together with photographs of the skeleton. Interesting results were obtained in regard to the phenomena of wireless telegraphy along this same line of electrical work.

Since the attention of physicians is now directed to the curative effect of the ultra violet rays in certain forms of skin diseases, investigation was started by Professor Trowbridge upon the relative activity of these rays in the vapors of different metals. The method of study is an entirely new one and is only made possible by the aid of the large battery in the laboratory. An investigation was also taken up at the same time, on the subject of magnetism--to decide what degree of alternating current will reduce iron to a state of copper as far as magnetism is concerned. These two experiments are still in progress.

Several other important experiments carried on by the department during the year have been published in scientific magazines.