400 PHILOSOPHICAL SOCIETY OP WASHINGTON. 
The paper was discussed by Messrs. Eathbun, Tittmann, and 
We ad. 
Mr. E. B. Bosa then, by invitation, with the aid of lantern 
views, described the Plans for the buildings of the National 
Bureau of Standards. He spoke of the many conveniences pro¬ 
vided for work, and of the provisions for the avoidance of mag¬ 
netic and mechanical disturbances, of dust, and of changes of 
temperature. [Published in Science, Jan. 23, 1903.] 
557th Meeting. November 8, 1902. 
President Eathbun in the chair. 
Thirty-eight persons present. 
Mr. C. G. Abbot exhibited and explained A device to obtain 
time signals of variable intervals from a uniform-motion clock¬ 
work. The clockwork drives in reverse directions t^yo discs, with 
either of which a shaft may be connected by electromagnetic 
clutches; this shaft carries a radially extending switch-arm which 
swings between two contact devices. One clutch being engaged 
and the shaft rotating, ultimately the arm strikes one contact 
device; this switches the current to the other magnet and re¬ 
verses the rotation of the shaft. The instants of reversing are 
noted on the chronograph sheet. The angle between the contact 
devices is adjustable to vary the interval, and the support which 
carries them may be moved to accelerate or retard the time of 
reversal. The attachment was designed primarily for use in Mr. 
Langley’s method of eliminating personal equation in transit 
observations. [Not published.] 
The communication was discused by Messrs. Bigelow, Briggs, 
Marvin, IIayford, Wead, and Littlehales. 
Mr. W. J. Spillman then presented the Theory of combina¬ 
tions applied to Mendel’s law. This law expresses the probable 
character of hybrids and their progeny. As the number of 
features in which the parents differ increases, and the number 
of generations, the number of possible combinations of these 
features becomes very great; but ultimately the progeny reduce 
practically to the two parent types and a very few new types. 
Lantern illustrations showed the results from crossing of varie- 
