March 20, 1896.] 



SCIENCE. 



455 



form of electric light; for example, with a 

 heliostat and condensing system he was able to 

 project the interference bands of the Fresnel 

 bi-prism upon a screen so that they were visible 

 across a large room. Prof. Mayer's heliostat 

 consists in a clockwork driving a shaft parallel 

 to the earth's axis ; upon the southern end of 

 the shaft is the mirror that can either be twisted 

 on the shaft or set at any angle to the shaft. 

 The second mirror is mounted upon the base 

 with its central point in the prolongation of the 

 shaft. To orient the heliostat it is only neces- 

 sary to bring the side pieces in the north and 

 south line and then set the mirror on the clock 

 axis. This last is done by covering the elliptical 

 mirror with a paper having a S-inch hole in 

 the center, and adjusting the tilting mirror 

 until the small beam of light reflected from the 

 mirror through the hole falls upon the center 

 of the mirror attached to the base of the instru- 

 ment ; then starting the clock, the instrument 

 will keep the beam in a constant direction. 

 Prof. Hallock in discussing the paper called at- 

 tention to the accuracy with which the heliostat 

 operated, and related his experience with a 

 very large one-mirror heliostat in the Smith- 

 sonian Institution at Washington, which, how- 

 ever, was thoroughly unsatisfactory. Prof. 

 Woodward and Prof Jacobi also entered into 

 the discussion of the relative merits of the 

 various heliostats, especially the typical one- 

 mirror and two-mirror heliostats. 



Prof. M. I. Pupin then brought before the 

 academy some recent observations he had made 

 while experimenting with X-rays. In the first 

 place, he pointed out that certain Crooke's tubes 

 after a certain amount of use had their vacuum 

 improved, so that the induction spark passed 

 outside the tube rather than through the tube. 

 Prof. Pupin was at a loss to altogether explain 

 the cause, but believed that it might be due to 

 the condensation of some of the gas remaining 

 in the tube, and explained several experiments 

 which he had already made confirming the ob- 

 servation that the vacuum was improved with 

 use, and that in proportion as the vacuum im- 

 proved the tubes were better for X-ray pho- 

 tography. Another phenomenon observed by 

 him was that in developing the photographic 

 plates the development began at the glass side 



of the film, leading to the inference that the 

 X-rays penetrated the film and rendered the 

 glass fluorescent, this fluorescent light then 

 acting upon the film. Following the sugges- 

 tion of this observation he painted the inside 

 of a box with the platinum-barium-cyanide and 

 laid a photographic plate against it, making a 

 photograph then through the side of the box. 

 The X-rays develop the fluorescence in the 

 cyanide which fluorescent light afiects the plate. 

 In this way he obtained very good results with 

 much shorter exposures than by the original 

 method. W. Hallock, 



Secretary of Section. 



BOSTON SOCIETY OF NATURAL HISTORY. 



A GENERAL meeting was held February 19th, 

 thirty persons present. Mr. A. W. Grabau 

 showed a specimen of the broad variety of Para- 

 doxides harlani Green from a third locality in 

 South Braintree. 



Prof A. Hyatt called attention to several 

 shadowgraphs taken in Germany by Mr. R. W. 

 Wood. One of them shows plainly the bones, 

 the position and outline of the lungs, heart and 

 ossophagus of a mouse, and indicates the possi- 

 bilities of the ray as an aid to natural history 

 studies. 



Mr. Outram Bangs read a paper on the terra- 

 pin {Malaelemys terrapin Schoefi") as an inhabi- 

 tant of Massachusetts. This species has been 

 known for fifteen years as occurring in the 

 creeks and salt marshes of Buzzard's Bay. It 

 was formerly very abundant, but has lately be- 

 come quite scarce. A comparison of the Buz- 

 zard's Bay material with a series from the At- 

 lantic coast from Washington to Florida and 

 from Mobile shows variations in color, marking, 

 roughness of the shell, and in the size and shape 

 of the skull. These variations, however, are 

 not considered sufiicient to form a separate 

 race. The evidence that the terrapin is not 

 native to Buzzard's Bay, but was introduced, 

 was considered insufficient. 



Dr. Joseph Lincoln Goodale spoke on the 

 vocal sounds of animals and the mechanism of 

 their production. He described the simplest 

 type of larynx ; also the four principal types, 

 mentioning the best examples of each type. 

 The three characteristics of sound were noted, 



