September 19, 1884.] 



SCIENCE, 



293 



oids have the same reflecting power as Yesta, Pro- 

 fessor Harrington reaches the conclusion that the 

 volume of Yesta is about fV that of all these 230 

 bodies put together, and that Yesta and Ceres to- 

 gether form almost one-half the total volume. 



Professor Rogers of the Harvard college observatory- 

 then read two papers. The first one, upon the mag- 

 nitude of the errors which may be introduced in the 

 reduction of an observed system of stellar co-ordi- 

 nates to an assumed normal system by graphic meth- 

 ods, showed a great amount of laborious research, 

 and was a good illustration of the vast amount of 

 monotonous work necessary in the present stage of 

 astronomical observation in order to reach the highest 

 degree of accuracy attainable by the search for and 

 elimination of minute systematic errors. His next 

 paper was upon the original graduation of the Har- 

 vard college meridian circle in situ. This described 

 a method of turning a meridian circle through any 

 desired constant arc up to about 30° without any 

 dependence upon the circle and reading microscopes, 

 effected by means of an arm swinging between fixed 

 stops, and clamping to a circular ring on the axis by 

 an electro-magnetic clamp. With this Professor Ro- 

 gers claimed to be able to set off a constant arc through 

 as many as five thousand successive movements of 

 the clamping arm. The ingenious method suggested 

 and carried out by Mr. George B. Clark, of the firm 

 of Alvan Clark & Sons, of grinding the clamping 

 circle to a perfect circular form while the telescope 

 was swung round in its Y's, was fully described, and 

 also Professor Rogers's method of arresting the mo- 

 mentum of the telescope at the stops by water-buffer 

 plungers. The great advantage of thus being able to 

 set off a constant arc independent of the circle and 

 microscopes was pointed out, with especial reference 

 to the investigation of division errors and flexure of 

 circle, and also to the division of the circle itself in 

 situ; i.e., mounted on its axis and turning on its 

 pivots. Professor Young called attention to the 

 necessity of guarding against expansion and contrac- 

 tion of the bar holding the stops, due to radiation 

 from the observer's body. 



Mr. S. C. Chandler, jun., of the Harvard college 

 observatory, gave the results of observations and ex- 

 periments with an ' almucantar ' of four inches aper- 

 ture, a new instrument devised by Mr. Chandler, 

 which seems to be of remarkable accuracy, and 

 promises to furnish an entirely new and independent 

 method of attacking some of the most important 

 problems in exact observational astronomy. The in- 

 strument consists of a telescope and vertical setting- 

 circle, which can be clamped at any zenith-distance, 

 and is supported on a rectangular base which floats 

 in a rectangular trough of mercury, the whole turn- 

 ing round a vertical axis so as to observe in any 

 azimuth; these observations being simply the times 

 of transit of any heavenly body over a system of 

 horizontal wires in the field. The observations thus 

 far have been entirely upon stars, and all at the 

 apparent zenith-distance of the pole. After some 

 very small periodic variations in the zenith-distance 

 pointing had been traced to changes of temperature, 



and had been removed by sawing through the wooden 

 bottom of the mercury trough, the instrument showed 

 an astonishing constancy in this zenith-distance 

 pointing, extending over weeks at a time, and far 

 exceeding the constancy of the corrections to the 

 best fundamental instruments of our observatories. 



A paper was read by Mr. Chandler, upon the colors 

 of variable stars. Showing, first, that most of the 

 variables were red, he described some fairly satis- 

 factory methods which he had used to measure the 

 degree of redness of all the periodic variables; and 

 then, plotting a series of points whose abscissae 

 represented the length of the periods, and ordinates 

 the degree of redness, their agreement with a curve 

 making a very decided angle with the axis of abscis- 

 sae brought out without question the remarkable 

 law, that, the redder the star, the longer is its period 

 of variability. In discussing any theory of variable 

 stars, Mr. Chandler pointed out that Zollner was the 

 only one who had thus far taken into account two 

 laws already known: viz., 1° that they are generally 

 red; 2° that they increase in brightness much more 

 rapidly than they decrease ; and now, in any further 

 theory, this new third law must have a place, viz., 

 that, the redder they are, the longer is their period. 



Monday's session opened with a paper by Dr. R. 

 S. Ball, astronomer royal of Ireland, upon the 

 ruled cubic surface known as the cylindroid, whose 

 equation is 



z (x 2 + y 2 ) — 2mxy = 0. 



Mr. W. S. Auchincloss of Philadelphia exhibited 

 a balancing-machine for finding the centre of gravity 

 of any number of different weights distributed along 

 a line, which seemed to be of excellent construction, 

 extremely easy and rapid in manipulation, and quite 

 sensitive. In connection with a time-scale of three 

 hundred and sixty-five days at one side, it was shown 

 how rapidly a complicated system of business accounts 

 could be settled, and how it could be applied to various 

 engineering problems. 



The next paper was by Prof. J. H. Gore, of the 

 U S. geological survey, upon the geodetic work of 

 the U. S. coast and geodetic survey. This was a 

 long paper, much of it devoted to a historical resume 

 of geodetic work in all countries. The points of 

 principal interest brought out were the great advan- 

 tages possessed by the United States in its vast ex- 

 tent of territory, for determining the figure of the 

 earth; and the work already done along the coasts, 

 and along a chain of triangles from the Atlantic to 

 the Pacific, was shown on a map. The great accu- 

 racy attained, especially in base-measurement, was 

 noted, and the great improvements made in apparatus 

 and instruments of the survey. Especially was the 

 importance insisted on of a scientific body like the 

 American association supporting in every way the in- 

 tegrity and unity of this great work. In answer to 

 questions, Professor Gore stated that the most recent 

 improvements in the base-measuring apparatus were 

 the determination of the coefficients of expansion 

 for every degree of temperature to which they would 

 be exposed ; and he expressed his belief that results 



