AuoDST 24, lti83.] 



SCIENCE. 



237 



ber of the solar system, exact data will determine the 

 exact position in orbit at a given time; but here we 

 have neither exact data, nor can we ennjloy trigono- 

 metrical methods in the solution. We simply Hnd 

 that the observed proper motions are probably .-o'me- 

 what better reconciled under the hypothesis o( an as- 

 sumed postilion of the apex o( the solar motion. The 

 method of investigation employed by Safford, who 

 has of late years given much attention to this sub- 

 ject, consists in assuming a system of co-ordinates 

 for the pole of the solar motion, from which is deter- 

 mined the direction each star wouhl have if its own 

 proper motions were zero. Comparing this direction 

 with the observed direction as indicated by the ob- 

 served proper motion, equations of conditinn are 

 formed from which a correction is found to the .as- 

 sumed position of the apex, by the methods of least 

 si|uares. 



It must always be kept in mind, that the quantities 

 with which we must deal in this investigation are 

 exceedingly minute, and that the accidental errors of 

 observation are at any time liable to lead to illusory 

 results. The weak link in the chain of Miidler's 

 reasoning is to be found here. I think we can as- 

 sume 0.2" as the limit of precision in the absolute 

 determination of the co-ordinates of any star, how- 

 ever great the number of observations upon which it 

 depends. Beyond this limit it is impossible to go, 

 in the present date of instrumental astronomy. 



It is safe to say, that there is not a single star in 

 the heavens whose co-ordinates are known with cer- 

 tainty within this limit. Do not misunderstand me. 

 Doubtless there are many stars in which the error 

 will at some future time be found to fall within this 

 limit. The law of probabilities requires this, if the 

 maximum limit falls within 1". But who is prepared 

 to select a particular star, and say that the absolute 

 position of this star in space cannot be more than 

 0.2" in error ? 



e. At present an arbitrary hypothesis is necessary 

 in the discussion of the problem. Airy assumed that 

 the relative distances of the stars are proportional to 

 their magnitudes; and he found slightly different 

 results according to different modes of treatment. 

 Safford assumed that the distances are, at least ap- 

 proximately, in inverse proportion to the magnitude 

 of the proper motions. The general result of his 

 investigations, up to this point, is, that there is some 

 hope of using the solar motion .as a base, to advance 

 our knowledge of stellar distances. Later investiga- 

 tions have been made by De Ball, but the details 

 have not yet come to hand. It is understood, how- 

 ever, that his results coincide in a general way with 

 those previously obtained. 



It is clear from this brief review, that we have 

 here a field of investigation worthy of the highest 

 powers of the astronomer. The first step has been 

 taken in the survey of the heavens carried on under 

 the auspices of the gesellschaft. It remains for the 

 astronomers of the present generation to solve the 

 difficulties which now environ the problem, and pre- 

 pare the way for a more perfect scheme of observation 

 in the next century. 



PAPERS READ BEFORE SECTION' A. 



The total solar eclipse of May 6, 1883. 



BY EDWAltU S. IIOIDEN, OK W.\SIIBU11N OUSUBVA- 

 TOKV, M.VDISON, WIS. 



Tnis eclipse had the longest totality of any which 

 has been observed. 



An expedition was sent by the Kational academy 

 of sciences and the U. S. coast-survey jointly, under 

 direction of a committee from the former. Ex- 

 penses were met by an appropriation of S."),000 by 

 congress and by the National academy of sciences 

 from a fund left by Professor Watson. The navy 

 department also placed the U. S. steamer Hartford 

 at the disposal of the academy, to transport the ex- 

 pedition from Peru to Caroline island, where tlie 

 eclipse was to be observed, and thence to Honolulu. 



The efforts of Mr. Rockwell to provide money by 

 private subscription for this undertaking, thougli 

 directly unsuccessful, prepared the way by drawing 

 public attention. 



Professor Young was the chairman of the com- 

 mittee of the National academy of sciences: it was 

 at one time hoped that he would take charge of 

 the observing-party, but this proved impracticable. 

 The reports of different members of the party are to 

 be submitted to the National acideniy of sciences in 

 November. Mr. Holden lias, however, permission of 

 the academy to present an account of the observation 

 before the American association. It is understood 

 that the present is not by any means a final report. 

 This especially applies to the observations of Dr. 

 Hastings, from which that gentleman concludes 

 that the solar corona is chielly a phenomenon due 

 to the diffiaction of the solar light at the moon's 

 limb. The computations to demonstrate this are 

 not yet at hand, but are to be completed in a few weeks. 



Tlie American party consisted of Eilward S. 

 Holden, director of Washburn observatory, Madison, 

 Wis.; Cliarles S. Hastings, professor of physics in the 

 .Johns Hopkins university, Baltimore, Md. ; Charles 

 H. Kockwell, Tarrytown, N.Y. ; E. D. Preston, aid 

 U. S. coast and geodetic survey, Washington, D.C. ; 

 Winslow Upton, U.S. signal-office, W.ashington, D.C. ; 

 and Ensign S. J. Brown, U.S.N., U. S. naval observa- 

 tory, Washington, D.C' 



The original six members of the parly were joined, 

 on April 20, by four volunteer observers, all officers 

 of the U.a. ship Hartford: these were Lieut. E. F. 

 Qualtrough, U.S.N. ; I'assed assistant-surgeon W. S. 

 Dixon, U.S.N. ; Midshipman W. S. Fletcher, U.S.N. ; 

 and Midshipman J. G. Doyle, U.S.N. 



On March 11 the party was strengthened by the 

 joining (at Colon) of the two English gentlemen who 

 were sent out by the Itoyal society of London to 

 make photographic observations of the eclipse, under 

 instructions from .1. Norman Lockyer, Esq., F.Il.S., 

 and Capt. W. de W. Abney, K.E., of the science and 

 art depart uicnt of the .South Kensington museum. 

 These were H. A. Lawrance, London, Eng., and 

 C. Kay Woods, London, Eng. 



During the slay of the party on Caroline island 



