October 27, 1892] 



NATURE 



613 



least) was obtained by continuing the observations of the 

 btars throughout the whole of the year, that is, to secure 

 observations in all positions of the parallactic ellipse. If 

 the measures were confined to those epochs when the 

 parallactic displacements were greatest, and a sufficient 

 number of observations secured at those critical times, a 

 determination of parallax could be relied upon to within 

 about one-thirtieth of a second of arc. This is approxi- 

 mately the limit of accuracy that Professor Pritchard 

 hoped to reach, and in this selection he appears to have 

 been guided by the conviction, that in the present condi- 

 tion of cosmical inquiries, to which stellar parallax bears 

 the closest relation, it is of more importance to know within 

 very narrow limits the parallaxes of many stars than 

 seek with the utmost accuracy the parallax of a very few. 

 And in this respect there can be no doubt but that Prof. 

 Pritchard's judgment is correct. The former is the view 

 of a philosopher ; the latter that of a conscientious and 

 painstaking observer. Guided by the broader view, the 

 result of his work has been to enrich the data at the com- 

 mand of students of cosmical science by assigning the 

 approximate distance to some thirty stars, a number which 

 bears no inconsiderable proportion to the total number of 

 separate determinations made by all other astronomers 

 combined. 



Prof. Pritchards view of the history of stellar parallax 

 is that of a scientific struggle, a continual and severe 

 wrestle on the part of the astronomer with the inevitable 

 inaccuracy of observation and imperfect instruments, in 

 which sometimes one opponent, sometimes the other, has 

 the mastery. He passes in his historic survey rapidly 

 over those days when from various obvious causes the 

 detection of stellar parallax was scarcely possible, moved 

 however to admiration by, and induced to linger over, 

 the success that attended the early observations of 

 Molyneux in the case of y Draconis when discussed, 

 a century later, by Auwers, a success that later observers 

 have struggled to repeat ineffectually. He brings before us, 

 but touches with a light and kindly hand, the dispute 

 that embittered the lies of Brinkley and of Pond, but it 

 is not difficult in reading a little between the lines to see 

 with whom his sympathies rest. Later on in the history 

 of the research, Henderson meets with his deserts, as a 

 clear-sighted astronomer of distinguished ability, cautious 

 and persevering, and one who in the struggle after accu- 

 racy obtained an undoubted measure of success. This 

 historical introduction will we think be read with pleasure 

 by many whomay have no particularinterest in this special 

 subject of inquiry. The comments of one who has en- 

 countered and overcome many similar difficulties, and 

 has kindly sympathy with all who have travelled along 

 the same path, cannot but be of interest and of value, and 

 we could have wished that this portion of the book had 

 been considerably extended. How many astronomers 

 are now acquainted, with any degree of adequacy, with 

 the serious difficulties that attended the early application 

 of the heliometer in this department of research, and 

 with the dispute that raged long and dubiously around 

 the names of Wichmann and of Schluter .^ All are 

 willing to admit that in the hands of many com- 

 petent observers— it would be invidious to mention 

 any without naming all — the heliometer is doing splendid 

 work, but the difficulties with which the early masters 

 had to cope are now all but forgotten, and it is certainly 

 wise to treasure a sympathetic remembrance for the 

 earlier exponents of the improved and successful methods 

 now in vogue. 



The last portion of Prof. Pritchard's history is occu- 

 pied with the bearing of stellar parallax on the problem 

 of the construction of the stellar universe. He seems 

 to have had before his mind two questions, which, 

 long hovering in an unexpressed form, were first for- 

 mally enunciated by Dr. Gill. The first question is, 

 What are the average parallaxes of stars of the first, 



second, third, and fourth magnitude respectively com- 

 pared with those of fainter magnitude .' To this ques- 

 tion the Savilian Professor replies very cautiously. The 

 researches of Dr. Elkin on stars of the first magnitude 

 point to an average parallax of o" 089 for stars of that 

 class, and just as certainly Prof. Pritchard's researches 

 point to an average parallax of o"o56 for stars of 

 the second magnitude. But he pertinently asks what can 

 be understood by an average of distances (as indicated by 

 parallaxes) in cases where the separate elements vary 

 from actual zero to half a second, and where moreover 

 many of the brighter members are the furthest removed 

 from us ? Notwithstanding these exceptional cases, which 

 challenge attention, the fact remains, and it is apparently 

 the only conclusion which can be drawn with any cer- 

 tainty, that the stars of the first magnitude are on the 

 whole nearer to us than those of the second, and that 

 these again are as a whole nearer to us than the faint 

 stars with which they have been compared. With con- 

 clusions of this sort it would seem that astronomers will 

 have to content themselves for some time to come. 



The second question which Dr. Gill suggested or for- 

 mulated was — What connection does there exist between 

 the parallax of a star and the amount and direction ot 

 its proper motion ? — or can it be proved that there is no 

 such connection or relation ? The answer given to this 

 second query is even less satisfactory than to the former. 

 Prof. Pritchard contents himself by exhibiting in a tabular 

 form the parallax and the proper motion of all stars that 

 have been successfully handled, and the only conclusion 

 drawn or warranted, is a suggestion that there is at least 

 quite as close a connection between the apparent proper 

 motion of a star and its distance from us, as there is be- 

 tween its distance and its magnitude. 



If we examine or attempt to trace any connection 

 between the mass, the brilliancy and the distance of a 

 star, we are baffled by the same kind of uncertainty, aris- 

 ing in some measure from the paucity of instances in 

 which it is possible to make the inquiry, and we are 

 reluctantly forced to admit that such investigations are 

 premature. At least that would be the conclusion of an 

 ordinary m-nd, but here it is that Prof Pritchard sees his 

 opportunity for future effijrts and renewed vigour. With 

 an energy that must be the admiration of his friends, he 

 selects for further investigation two subjects, either of 

 which might fully occupy the time and the hands of a 

 younger man. He proposes in the first place to determine 

 the parallaxes of several stars of the Pleiades, a few of the 

 brighter as well as a few of the fainter, with the view of 

 discovering whether the faint and the bright are indis- 

 criminately mixed at that distance. The second subject 

 of his proposed inquiry is not less interesting. It con- 

 sists in the investigation of the distances of some of the 

 binary systems from our sun ; and from a more complete 

 knowledge of the masses, the mutual distances, and the 

 parallaxes of these systems, Prof. Pritchard thinks it not 

 unlikely that many interesting and possibly unexpected 

 associations may reasonably be anticipated, thereby 

 affording us some further insight into the constitution and 

 the mechanism of the Stellar Universe. We can only 

 hope that Prof. Pritchard's health and strength may be 

 spared to witness the completion of this programme, but 

 in that case we are assured he would immediately sketch 

 out for himself some new field of inquiry, and court even 

 longer and more protracted labour. 



CONTRIBUTIONS TO THE STUDY OF 

 DISINFECTION} 



PROFESSOR J. MASCHEK, whose name is already 

 familiar to us through his investigations on water 

 bacteria, has brought together in pamphlet-form a large 



I " Beitrage lur Theorie und Praxis der Desinfeclion, von Prof. J. 

 Maschek." Im Selbstverlage det Verfassers, Leitmeritz. 



