160 



RECORD OF SCIENCE FOR 1886. 



with the 6-inch helioineter. He proposes to observe ten of the brightest 

 stars in the northern hemisphere for paraUax. Mr. A. Hall, jr., has been 

 engaged in observations of Titan with the heliometer, with a view to a 

 new determination of the mass of Saturn. 



Zurich (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. Hiltiker has determined the 

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

 meter in the atmospheric pressure — for. a Winnerl clock with gridiron 

 pendulum comparing the Winnerl clock with the H'pp 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 

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

 results obtained at Geneva and at several other observatories for their 

 normal clocks: 



(lUill. astron., December, 1886. 



The new optical glass, — Nature for October 28, 1886, contains an in- 

 teresting account of the experiments of Professor Abbe and Dr. 

 Schott in their endeavors to i>roduce a glass of such cliemical compo- 

 sition that it may be possible to make lenses free from the secondary 

 chromatic aberration and other defects. For the microscope lenses 

 already'made of the new glass Professor Abb6 claims great superiority 

 in many important respects. ■ 



Electric illumination. — Prof. Ormond Stone, of the McCormick»01)- 

 servatory, uses for illuminating the circles and micrometer wires of 

 the great equatorial, Edison incandescent lamps of one-caudle power, 

 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 re- 

 quired. The success of the experiment here has resulted in the us(i 

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

 other observatories. 



In the Greenwich spectroscopic observations, " a slip of metal coated 



