424 



NA TURE 



[August 29, 1901 



interest him concerning pearls, cameos and oysters. 

 The nomenclature has been, in the main, brought up to 

 date, the trumpet-shell figuring as Lotorium varicgatiim 

 in place of the familiar Triton trilonis^ while Scala, in- 

 stead of ^Crt/f/r/VijJstands for the precious wentletrap. 



A Text-book of Astronomy. By Prof. George C. 

 Comstock. Pp. viii-t-3gi. (New York and London : 

 D. Appleton and Co., 1901.) Price "js. 6d. net. 

 It is an e.xcellent sign that among recent works dealing 

 with astronomy there have been some in which methods 

 of teaching the elementary parts of the subject have 

 formed a notable feature. The book under notice is to 

 be regarded as one of this class, as the author, a well- 

 known American astronomer, has endeavoured to " con- 

 centrate attention upon those parts of the subject that 

 possess special educational value." The importance of 

 observations with simple appliances is strongly insisted 

 upon in the preface, but from this point of view the book 

 is distinctly disappointing. It is true that in the earlier 

 chapters an attempt is made to introduce practical 

 e.xercises, some of them observational and others in- 

 volving the construction or study of drawings ; but this 

 admirable beginning is by no means consistently followed 

 up. In fact, the greater part of the book does not strike 

 us as being other than a general outline of the chief facts 

 and principles of astronomy suitable for ordinary read- 

 ing, except that at intervals the reader is e.xpected to 

 pause and answer a cjuestion, such as " What is the 

 magnitude (of Algol) 43 days after a minimum?" The 

 practical method, however, might well have been further 

 adopted ; a telescope of adequate power for the demon- 

 stration of many phenomena, such as the sun's rotation, 

 can be cheaply and easily constructed, and graphical 

 exercises might have been more frequently introduced 

 with advantage. We notice, also, that the use of a globe 

 in illustrating celestial motions is not mentioned at all. 

 Nevertheless, so far as it goes, the practical work 

 described will be of great value to students, and will 

 doubtless encourage them to further efforts in the 

 same direction. 



The book touches upon nearly every branch of 

 astronomy, and the explanations and descriptions are 

 both concise and clear. The numerous illustrations have 

 been selected and reproduced with great care, and, as 

 the author remarks, are worthy of as careful a study as 

 the text : the diagram on p. 153, illustrating the path of 

 the moon with respect to the sun, deserves special 

 mention. 



An Introduction to the Practical Use of Logarithms. By 

 F. G. Taylor, M.A., B.Sc. Pp. vi -I- 63. (London : 

 Longmans, Green & Co., 1901.) Price \s. 6d. 

 There can be little doubt that much time is lost by 

 students and others who have occasion to make numerical 

 calculations through unfamiliarity with the practical 

 advantages of logarithms. In the present little book, 

 however, by the consistent employment of the simplest 

 arithmetical illustrations, the author goes far to remove 

 the mystery in which, to many students, the subject 

 appears to be involved by fuller theoretical treatment. 

 The explanations are clear throughout, and these, together 

 with the numerous carefully selected examples, should 

 enable a student of ordmary intelligence to quickly 

 master the use of logarithmic tables. The tables them- 

 selves occupy but six pages, two for logarithms, two for 

 reciprocals and two for anti-logarithms. A chapter on 

 methods of rough calculation, intended to verify the 

 results obtained by the use of logarithms, forms a valuable 

 addition to the book. The general subject is excellently 

 illustrated by the application to problems in mensuration, 

 and the whole is brought well within the range of students 

 who have no knowledge of algebra. 



NO. 1 66 1, VOL. 64] 



LETTER TO THE EDITOR. 



The Editor does not hold hitnse/f responsible for opinions ex- | 

 pressed by his correspondents. Neither can he undertake 

 to return., or to correspond ivitJi the writers of rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications.] 



The Moon and Wet Days. 



Though it is counted heresy in some quarters to associate 

 weather with the moon, the following results of a recent inquiry 

 into the subject, whether held to be proof of lunar influence or 

 not, might, I think, be of interest to many. 



The period considered is the last 24 years. The data 

 (which are for Greenwich) are these :^ 



(A) Days with "5 in. of rain, or more, in the year. 



(B) Days with '4 in., or more, in the summer half (April to 

 September). 



(C) D.ays with '2 in., or more, in the summer half. 



III I I I III I I I I I llll I I I M 



The method in each case was first to ascertain the distribution 

 in seven days about each of the four lunar phases {i.e. how 

 often each of those 28 days had rain amounting, e.g., to "5 in., 

 or more), then smooth the series with averages of three. 



Both smoothed and unsmoothed curves are given in the 

 case of A ; but only the smoothed curves for B and C. 



From the fact that four weeks does not quite cover the time 

 of a synodical revolution of the moon (which is about 29^ 

 days), there are a few wet days in each class not coming under 

 any of the above categories. These may perhaps, with regard 

 to the purpose of the inquiry, be left out of account. The totals 

 dealt with are : A, 182 days ; B, 15S ; and C, 433. These come 

 short of the actual totals by A, 7 days ; B, 8 ; C, 28. 



Turning now to the curves, the recurrence of four long waves 

 in the smoothed curve for A (less pronounced in C and B), may 

 be noted, in passing, as a remarkable feature. 



