598 



NA TURE 



{Oct. 1 6, i! 



fully described, and also Prof. Rogers' method of arresting the 

 momentum 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. 



Prof. Young called attention to the necessity of guarding 

 against expansion and contraction of the bar holding the stops, 

 due to radiation from the observer's body. 



Mr. S. C. Chandler, Tun., of the Harvard College Observa- 

 tory, gave the results of observations and experiments with an 

 " almucantar " of four inches' aperture, 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 ob- 

 servational astronomy. The instrument consists of a telescope and 

 vertical setting-circle, which can be clamped at any zenith-dis- 

 tance, and is supported on a rectangular base which floats in a 

 rectangular trough of mercury, the whole turning 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 tempera- 

 ture, 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 observa- 

 tories. 



A paper was read by Mr. Chandler, upon the colours of 

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

 red, he described some fairly satisfactory methods which he had 

 used to measure the degree of redness of all the periodic vari- 

 ables ; and then, plotting a series of points whose abscissa? 

 represented the length of the periods, and ordinates the degree 

 . their agreement with a curve making a very decided 

 angle with the axis of abscissa; brought out without question the 

 remarkable law thai Ihe 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. (i) 

 that they are generally red; (2) that they increase in brightness 

 much mort rapidly than th /and now, in any further 



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

 redder they a r e the longer is their period. 



Dr. R. S. Ball, Astronomer-Royal for Ireland, read a paper 

 upon the ruled cubic surface known as the cylindroid, whose 

 equation is 



- ( v- + _i~) - 2 in xy — o. 



Mr. W. S. Auchencloss of Philadelphia exhibited a balancing 

 machine foi finding the centre of gravity of any number of dif- 

 ferent weights distributed along a line, 'which seemed to be of 

 excellent cori extremely easy and rapid in manipula- 



tion, and quite sensitive. In connection with a time-scale of 

 365 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. 



Prof. J. H. Gore, of the U.S. Geological Survey, read a 

 paper upon the geodetic work of the U.S. Coast and Geodetic 

 Survey. 



The next paper was by Mr. J. N. Stockwell of Cleveland, 

 upon an analysis of the formula for the moon's latitude as 

 affected by the figure of the earth. In this Mr. Stockwell 

 claimed that Laplace's formula for expressing this was wrong ; 

 the question turning upon an approximate integration of a dif- 

 ferential equation, which he claimed to show was wrong by 

 separating into two terms a single one which expressed the dif- 

 ference of two effects, which, thus evaluated separately, became 

 either indeterminate or of an impossible amount. 



Prof. J. C. Adams of Cambridge, England, made some com- 

 ments upon Mr. Stockwell's paper, speaking in high terms of 

 the general work which Mr. Stockwell had done in the difficult 

 subject of the lunar theory ; but from such conclusions and 

 methods as those brought forward in this particular case he 

 said lie must express his total dissent. He then pointed out 

 that this equation was, to begin with, only an approximation ; 



that, before it could be treated at all as a rigorous one, many 

 other small terms must be included ; that, further, its integra- 

 tion was only an approximation ; and that in this case any 

 separation into terms, which, on a certain approximate assump- 

 tion, became either indeterminate or very large, was of no value 

 as a test of the equation. 



Prof. Ormond Stone, Director of the Leander McCormick 

 Observatory of the University of Virginia, gave an elaborate 

 description of that Observatory, now approaching completion, 

 and to be devoted entirely to original research. The telescope, 

 which will soon be mounted, is the twin in size of the Washing- 

 ton 26-inch, and like it in most of its details, except that the 

 driving clock is like that of the Princeton 23-inch, with an 

 auxiliary control by an outside clock, and that it has Burnham's 

 micrometer illumination. The Observatory has a permanent 

 fund of 76,000 dollars as a beginning, and iS.ooo dollars have 

 been expended in Observatory buildings, and 8000 dollars for 

 the house of the Director. Situated 850 feet above the sea, and 

 on a hill 300 feet above surroundings, the main building, circular 

 in shape, i- surmounted by a hemispherical dome 45 feet in dia- 

 meter. The brick walls have a hollow air-space, with inward 

 ventilation at bottom and outward at top. 



Mr. Warner, the builder of the dome, gave an interesting 

 description of the ingenious method of adjusting the conical sur- 

 faces of the bearing-wheels, so that they would, without guid- 

 ance, follow the exact circumference of the tracks ; and then of 

 the adjustment of the guide-wheels, so that the axis of this cone 

 should be exactly normal to the circular track. The framework 

 of tlie dome consists of thirty-six light steel girders, the two 

 central parallel ones allowing an opening six feet wide. The 

 covering is of galvanised iron, each piece fitted in situ, and the 

 strength of the frame is designed to stand a wind-pressure of a 

 hundred pounds per square foot. There are three equal openings 

 with independent shutters, the first extending to the horizon, the 

 second beyond the zenith, and the third so far that its centre is 

 opposite the division between the first and second. The shutters 

 are in double-halves, opening on horizontal tracks, and con- 

 nected by endless chain with compulsory parallel motion of the 

 ends. The dome weighs twelve tons and a half, and the live- 

 ring one ton and a half, and a tangential pressure of about forty 

 pounds, or eight pounds on the endless rope, suffices to start it. 

 If this ease of motion continues as the dome grows old, it is cer- 

 tainly a remarkable piece of engineering work. 



In the discussion following, Prof. Hough thought he should 

 prefer the old style of single opening extending beyond the 

 zenith. 



Prof. Stone could not agree with him, the greater extent of 

 opening making it less probable that the dome would have to be 

 moved so far in turning from star to star, and at the same time 

 furnishing better ventilation, and the opportunity for cross- 

 bracing adding strength to the dome. He stated that he should 

 fust take up the remeasurement of all the double stars of less 

 than 2" distance between 0° and - 30 . 



The Rev. Father Perry, the Director of the Observatory at 

 Stonyhurst, England, gave the result of late researches on the 

 solar surface, with special reference to evanescent spots. 



Mr. Lewis Swift, Director of the Warner Observatory at 

 Rochester, N.Y., read a paper upon the nebulae, in which he 

 described his method of search for new nebulae. One very 

 interesting statement of Mr. Swift, to the effect that there had 

 not been a first-rate clear sky since the red glows appeared a 

 year ago following the Krakatoa explosions, bears out the 

 general experience of workers in other observatories, especially 

 those who try to see stars near the sun in the daytime. 



An interesting discussion arose as to the much-disputed exist- 

 ence "I the nebula round the star Merope in the Pleiades ; the 

 general drift of it being that the nebula no doubt existed, but in 

 order to see it a clear sky was necessary, and a very low power 

 and large field, so that the nebula might be contrasted with 

 darker portions of the same field ; that a large telescope was not 

 necessary, in fact the smaller the better, provided the optical 

 qualities were relatively as good. Mr. Swift said he could 

 always see it under favourable conditions ; and Mr. E. E. 

 Barnard, of Nashville, Tenn., the discoverer of the latest comet, 

 said that before he knew of its existence at all, he picked it up 

 as a supposed comet. 



Prof. Adams of Cambridge, England, read a paper upon the 

 general expression for the value of the obliquity of the ecliptic at 

 any given time, taking into account terms of the second order. 

 The difficulties of obtaining a formula for this quantity, on 



