SCIENCE. 



447 



of the head ; the nucleus was small and not very well 

 defined. 



This comet differs considerably in general appearance 

 from the comet now in ursce minor. The head of B was 

 large and broad, and its tail spread out greatly. Comet 

 C has a small, narrow head with a very long slender 

 shaft-like tail running from it in a straight line. 



E. E. Barnard. 



Nashville, Tenn., August 26. 



JUPITER. 



The following cut represents the planet Jupiter on 

 October 21st and October 29th, 1879, as seen with the 

 18 y z inch Chicago refractor, with power 638. 



The numbers on the right indicate the faint belts, 

 which were systematically arranged on either side of the 

 planet's equator. 



The great Equatorial Belt, crossing the center of the 

 disc, was composed of two separate belts, being divided 

 by an irregular rift extending through the central por- 

 tion. The color of this belt was reddish-brown-brick 

 color, and the total width was 15,780 miles. 



The great red spot shown in the center of the disc, on 

 October 29th, was essentially of the same color as the 

 equatorial belt, only more brilliant ; it was about 30,000 

 miles in length and 8000 in breadth. Under fair atmos- 

 pheric conditions, the equatorial belt was always visible 

 up to the edge of the disc, with very slight diminution of 

 color. 



CORRESPONDENCE. 



COMET b., 1 88 1. 



Harvard College Observatory, ) 

 Cambridge, U. S. September 13, 1881. f 



To the Editor of " Science." 



Sir: — The spectrum of comet b, 1881, according to 

 Dr. Konkoly (Observatory, 53, p. 257) contains five 

 bright bands. From the mean of measures made with dif- 

 ferent spectroscopes on different nights, their wave- 

 lengths in millionths of a millimetre were found to be 

 560, 545, 515, 472 and 468. The first, third and fourth of 

 these bands are evidently due to carbon and, as Dr. Vogel 

 has shown, are coincident with those of the banded stars 

 of Secchi's fourth type. The other two bands appear to 

 coincide with those of LI. 13412. Last winter the spect- 

 rum of this star was found to consist mainly of bands 

 having wave-lengths 545, 486 and 466 (Nature, xxiii, 604). 

 The line 486 is probably due to hydrogen. The singular 

 kinship of comets and banded stars is thus confirmed 

 by a star whose spectrum seems to be quite unique. 



Edward C. Pickering. 



To the Editor of " Science." 



About two weeks ago, I found that one of the turtles 

 which I keep for experimental purposes, a Chrysemys 

 picta had laid eggs; all but one of these had been de- 

 voured whether by the turtle itself (as I have known 

 to be the case with the same species, when kept in cap- 

 tivity) or by some alligators living in the same tank I 

 could not discover. The perfect egg, I imbedded in 

 moist sand, after carefully washing it, and finding yes- 

 terday, that it had not undergone development, I opened 

 it and to my surprise found a living maggot, the larva 

 probably of the Musca vomitoria, creeping around ac- 

 tively in the space between the half dessicated yolk and 

 the shell membrane. It measured about four millimeters 

 in length. As it crawled out of the aperture in the shell 

 which I had made I threw the specimen away as it did 

 not show the original anomoly. 



Analogous observations have been made in the chick's 

 egg. Cases are not infrequent where one egg has en- 

 closed another or even several eggs, legs of beetles, wisps 

 of straw and other foreign bodies. But this is I believe 

 the first case where a living animal has been found in an 

 egg. Of course the explanation of its presence is the 

 same as in the case of the other substances referred 

 to. E. C. Spitzka. 



BOOKS RECEIVED. 



Elements of Algebra, by G. A. Wentworth, A. 

 M., Professor of Mathematics in Phillips 

 Exeter Academy, 8° Boston. Ginn & Heath, 

 1881 ; viii, 380 pp. 



This addition to American a gebraic literature is the 

 sort of book that is to be expected from a live teacher. 

 It bears the stamp of experience upon it and gives evi- 

 dence throughout of the one end and aim of teaching 

 beginners in algebra the art of algebraic manipulation. 

 We say the art rather than the science, because the aim 

 is clearly to familiarize the pupil with the art, to teach 

 him how to manipulate rather than to lay stress upon 

 the reasons for the processes, the author being evidently 

 a disciple of Thomas Hill in his belief " Facts before 

 reasoning." This is shown by such statements as 

 " From these it may be assumed, etc."; " It may be veri- 

 fied that, etc. " 



The author has paid " particular attention to brevity 

 and perspicuity in definitions," a thing which cannot be 

 too highly commended, and without which any algebra, 

 however good in other respects, will not succeed. 



This matter of definitions is, as every teacher under- 

 stands, a very important matter, if not for the algebra it- 

 self, then at least as a matter of right training and clear 

 thinking. Definitions should be memorized, but memor- 

 ization is not enough ; they must be thoroughly under- 

 stood. With those teachers who do not agree with this 

 view we will have no disagreement, for the student 

 trained to thoroughly comprehend is generally found by 

 that very process to have secured that definition in his 

 memory. In a text book, therefore, which aims at clear- 

 ness and brevity in definition, a valuable training is 

 afforded the student by leading him to carefully weigh 

 the definitions ; to consider whether the definition can be 

 curtailed without loss of clearness, or whether it be not 

 already too brief to be intelligible ; to consider whether 

 it is too restricted or too extended in its application, etc. 



With the view of emphasizing this important matter 

 we shall call attention to some of the definitions in this 

 book, and at the outset let us premise that the definitions 

 of mathematical terms must conform to the usage of ma- 

 thematicians. It is a well-known fact that certain fea- 

 tures of text books, faults as well as excellencies, are 

 faithfully reproduced. Witness the statement concerning 

 the rotation period of one of the major planets, erron- 

 eously given in one of the earlier editions of" Herschell s 

 Outlines," and this error faithfully copied into astrono- 



