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SCIENCE. 



[Vol. IV., No. 85. 



more accurate still would be attained by immersing 

 them in melting ice, so as to keep them at a constant 

 temperature when in actual use. 



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 differential 

 equation, which he claimed to show was wrong by 

 separating into two terms a single one which ex- 

 pressed the difference of two effects, which, thus 

 evaluated separately, became either indeterminate or 

 of an impossible amount. 



Prof. J. C. Adams of Cambridge, England, made 

 some comments upon Mr. Stockwell's paper, the au- 

 dience eagerly crowding forward that they might lose 

 none of the interesting discussion. Professor Adams 

 spoke 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 he must express his total dissent. He then, in 

 the simple yet forcible manner of a master of mathe- 

 matical analysis, 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 inte- 

 gration was only an approximation; and that in this 

 case, any separation into terms, which, on a certain 

 approximate assumption, became either indetermi- 

 nate or very large, was of no value as a test of the 

 equation; that, in the case of oculating elements re- 

 ferred to by Mr. Stockwell, tbese in no sense repre- 

 sented an average orbit, but only an instantaneous 

 state of ever-varying elements; and that any integra- 

 tion proceeding on the first hypothesis, over a long 

 period, would introduce an error increasing with the 

 time which would swallow up entirely the perturba- 

 tions sought. The celebrated astronomer, than whom 

 neither England nor the whole continent of Europe 

 could have sent one more competent to advise, then 

 closed with a few remarks pregnant with suggestion 

 to workers in the lunar theory, upon the general 

 methods to be followed in these long and difficult 

 solutions by approximations. Hearty applause fol- 

 lowed; and the animated discussion was brought to 

 a good-natured close, Mr. Stockwell still unconvinced, 

 hoping that when Professor Adams had given more 

 attention to this particular point, he would come to 

 think the same of it as himself; and Professor Adams 

 (amid much laughter) hoping that day would never 

 come. 



In Tuesday's session, Professor Ormond Stone, 

 director of the Leander McCormick observatory of 

 the University of Virginia, gave an elaborate descrip- 

 tion 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 Washington twenty-six inch, and like 

 it in most of its details, except the driving-clock, 

 which is like that of the Princeton twenty-three inch, 

 with an auxiliary control by an outside clock, and 



that it has Burnham's micrometer illumination. The 

 observatory has a permanent fund of seventy-six 

 thousand dollars as a beginning; and eighteen thou- 

 sand dollars have been expended in observatory build- 

 ings, and eight thousand dollars for the house of the 

 director. Situated eight hundred and fifty feet above 

 the sea, and on a hill three hundred feet above sur- 

 roundings, the main building, circular in shape, is 

 surmounted by a hemispherical dome forty-five feet in 

 diameter. 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 inter- 

 esting description of the ingenious method of adjust- 

 ing the conical surfaces of the bearing-wheels, so that 

 they would, without guidance, follow the exact circum- 

 ference 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 frame- 

 work of the dome consists of thirty-six light steel 

 girders, the two central parallel ones allowing an 

 opening six feet wide. The covering is of galvanized 

 iron, each piece fitted in situ, and the strength of the 

 frame is designed to stand a wind-pressure of a hun- 

 dred pounds per square foot. There are three equal 

 openings with independent shutters, the first extend- 

 ing 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 certainly a remarkable piece of engineering work. 



In the discussion which followed, Professor Hough 

 said that he should prefer the old style of single open- 

 ing extending beyond the zenith. Professor Stone 

 could not agree with him, the greater extent of open- 

 ing 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 first take up the 

 re-measurement of all the double stars of less than 2" 

 distance between 0° and —30°. 



Father Perry, the director of the observatory at 

 Stonyhurst, Eng., gave the result of late researches 

 on the solar surface, with special reference to evanes- 

 cent spots. No abstract can give any idea of the 

 wide range of interesting topics covered in this paper. 

 The multitude of ever-changing details to be observed 

 on the sun, and the careful record of these which is 

 kept at the Stonyhurst observatory, furnished the 

 material for a paper replete throughout with new and 

 important details, to which nothing but a publication 

 in full can do any justice whatever; and it is to be 

 hoped that the association will soon give the public 

 the opportunity to read it in this way. 



On Wednesday, Mr. Lewis Swift, director of the 

 Warner observatory at Rochester, N.Y., read a paper 

 upon the nebulae, in which he described his method 



