160 



RECORD OF SCIENCE FOR 1886. 



with the G-iiicli lieliomoter. lie proposes to observe ten of the brightest 

 stars iu the northern hemisphere for parallax. Mr. A. llall, jr., has been 

 engaged iu observations of Titan with the hcliometer, with a view to a 

 new determination of the mass of Saturn. 



Ziirich (1885). — Dr. Eudolf Wolf is occupied almost entirely with sun- 

 spot statistics. He fixes the last "maximum" of spots at 188.3.9. 



ASTRONOMICAL INSTRUMENTS. 



Barometer coefficients for clods. — Dr. Hilfiker has determined the 

 barometric coefficient — or tlie variation in rate for a change of 1 milli- 

 meter in the atmospheric pressure — for a Winuerl clock with gridiron 

 pendulum comparing the Wiunerl clock with the H'p]) normal electric 

 clock at Neuchatel on each night of observation. 



These comparisons, made between August, 1884, and September, 

 1885, give an idea of the influence of the mode of compensation upon 

 the value of the barometric coefficient. The following table shows the 

 results obtained at Geneva and at several other observatories for their 

 normal clocks: 



Place. 



Noiicliatel 



Do 



rulkowa 



L('V(li311 



Berlin 



Ziirich 



Wiisbbuin Observatory. 



CompensatioH. 



Winuerl, gridiron pendulum. 



Hipp electric clock 



Mercury compensation 



dJ 



do 



do 



do 



Barometric 

 coefficient. 



0^ 010 

 0.012 



o.oi:j 



. 015 

 . 015 

 0.015 

 0.012 



(r>ull. astron., December, 1886. 



The new optical glass. — Nature for October 28, 18SG, contains an in- 

 teresting account of the experiments of Professor Abbe and Dr. 

 Schott in their endeavors to produce a glass of such chemical com}>o- 

 sition that it may be i)0ssible to make lenses free from the secondary 

 chromatic aberration and other defects. For the microscope lenses 

 already made of the new glass Professor Abbe claims great superiority 

 in many important respects. 



Electric illumination. — Prof. Ormond Stone, of the McCormick Ol)- 

 servatory, uses for illuminating the circles and micrometer wires of 

 the great equatorial, Edison incandescent lamps of one-candle i)o\ver, 

 run by what is known as the " Orne motor battery," or by the " Edco 

 battery," the latter being used where a more continuous light is le- 

 quired. The success of the experiment here has resulted in the use 

 of electricity, at least for circle illumination, at West Point, Yale and 

 other observatories. 



la the Greenwich spectroscopic observations, " a slip of raetal co^tetl 



