1896.] NEW YORK ACADEMY OF SCIENCES. 135 
The first business of the evening was the election of officers 
for the ensuing year. Professor Rees nominated R. 8. Wood- 
ward for Chairman and W. Hallock for Secretary. On motion 
the nominations were then closed, and the motion was put by 
Professor Rees to authorize Mr. Wade, as teller, to cast the 
ballot in favor of the gentlemen for the office named. The mo- 
tion was carried and the teller reported the vote cast.. 
The first paper of the evening was upon the apparatus designed 
by Professor W. L. Robb for showing the way in which a cord 
vibrates. It consisted essentially of an electro-magnet running 
a vibrating arm to the end of which the string is attached. 
The second paper was upon a new form of Polariscope, de- 
signed by Professor A. M. Mayer, consisting of a special ar- 
rangement of cross lenses resulting in unusually good illumina- 
tions and large field. 
The next paper was upon the Heliostat designed by Professor 
Mayer. In this connection Professor Mayer called attention to 
the shortcomings of the various forms of heliostat, and especi- 
ally those using only one mirror, pointing out, among other 
things, the useless width of mirrors on such heliostats and 
illustrating what ought to be the dimensions of such a mirror. 
He also called attention to the great advantage of using sun- 
light for all optical experiments over any 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 are 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 attached the mirror that can either be adjusted to 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 necessary 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 piece of paper having }$-inch hole in the 
center and adjusting the tilting mirror until the small beam of 
