22 



SCIENCE. 



which are present in the solar atmosphere. Oxygen is 

 included. Nitrogen is not. The point is here made that 

 the elements not present in the atmosphere of the sun are 

 precisely those which are most common on the earth, 

 and Mr. Lockyer's dissociation explanation is given and 

 a very full and fair s atement of the reasons for and 

 against it. 



We would have been glad to see in this place an ex- 

 amination of a paper by Dr. Hastings in the first number 

 of the American Journal of Chemistry, in which the 

 writer attempts to show that Lockyer's hypothesis is en- 

 tirely uutenable, and in conflict with received kinetic 

 theories of gases. 



The fourth chapter deals with the sun spots and the 

 solar surface. In this chapter is quoted a very remark- 

 able account of the phenomena attending the growth 

 and decay of a sun spot, written by that veteran obser- 

 ver of the sun, Dr. Peters, of Hamilton College. A foot 

 note to page 137 suggests a most interesting research in 

 relation to the acceleration or drift of the spots in long- 

 itude, and it is in such suggestions as this as well as in 

 its general views that the book will owe its great value to 

 the astronomical student. 



Chapter V. deals with the periodicity of sun spots and 

 with the theories as to their cause and nature. " On the 

 whole," Prof. Young says, " it seems probable that the 

 cause of the periodicity is in the sun itself " and is not 

 due to external causes. The relations of sun spots and 

 climate are discussed comple'ely, yet briefly. Professor 

 Young is one of the few English speiking astronomers 

 who can keep his temper upon this subject. 



In giving the various theories as to the cause and nature 

 of sun spots, the author deserves our thanks for a few 

 very simple diagrams, for the want of which many of us 

 have gone astray in reading the sun spot war records in 

 the Comples Rendus. 



The next chapter deals with the chromosphere and the 

 prominences, their appearances and the theories of their 

 formation and causes. 



In dealing with the lines of the chromosphere spectrum 

 we have two lists : First, those always present, and, 

 second, those readily seen by sutable manipulation 

 ("on slight provocation"). The catalogue of 273 lines 

 seen by Prof. Young at Sherman in 1872 is not given 

 here. The discussion of the causes of the great veloci- 

 ties observed in prominences on pages 211, 212 is es- 

 pecially interesting and suggestive. 



Chapter VII. is upon the Corona — its phenomena and 

 the theories of i s cause. The figure on page 225, with 

 its explanat'on on page 215, appear to the writer to give 

 too much weight to observations of a streamer in the 

 direction of the sun's poles at the solar eclipse in 1878. 

 It is not impossible that such a streamer existed, but it 

 seems at any rate very improbable in the light of the 

 photographs given in the Eclipse Volume of the Naval 

 Observatory. 



Chapter VIII. on the sun's light and heat is a rapid 

 survey of the important work which has been done on 

 these subjects. The light is first considered, and an ex- 

 pression for the sun's light in candle power deduced. 



Prof. Langley's interesting comparison of the light of 

 a Bessemer Converter to the sun's light is quoted as 

 showing the brightness of the sun to be over 5,000 times 

 that of the glowing metal. The positive carbon of the 

 electric arc is from two to four times f.iinter than the sun. 



The light from various portions of the sun's disc is 

 next considered, and the absorption of the light near the 

 limb brings us to the question of a so'ar atmosphere. 



This solar atmosphere has usually been considered as 

 gaseous, but the author quo'es Hastings' lately proposed 

 theory that this absorption is produced by matter in a 

 pulverulent condition at a lower temperature than the 

 photosphcric clouds and dispersed through the lower 

 portions of the sun's true atmosphere. 



" If the sun's atmosphere were removed, its brightness 



would be increased several times. It is almost certain 

 that the amount of light received by the earth would be 

 doubled ; it is hardly likely that it would be quintupled." 



The data as to the sun's heat are more precise ; and 

 the results of experiments (fully described) are put in a 

 striking way. The sun would meet in a single swing of 

 the pendulum a solid column of ice 2% miles in diameter 

 and 93,000,000 miles long, prov ded his whole power 

 would be concentrated upon it. What is the source of 

 this enormous energy which amounts to something like 

 one horse power continuously acting to each thirty square 

 feet of the earth's surface? Simple combustion of any 

 matter which we know would not suffice to keep up the 

 the sun's heat for any length of time. The effective 

 temperature of the sun is next considered, i. e., the tem- 

 perature which a uniform surface of lamp black of the 

 same size as the sun would have to keep, in order to 

 radiate the same quantity of heat as the sun itself. The 

 results of Rossetti (18,000° Fahr), are quoted with ap- 

 proval. The two most important theories as to the way 

 in which the solar heat is maintained — the meteoric the- 

 ory—and the contraction theory are next examined. 

 Both causes are undoubtedly operative. Probably the 

 contraction of the sun is the most effective agent. If 

 this theory be accepted then the sun has a limited future 

 as well as a finite past, so far as we can now see. 



Chapter IX. opens with a valuable table of numerical 

 data relating to the sun — a table of statistics for the solar 

 globe. 



The constitution of the solar nucleus and atmosphere 

 with an examination of various theories of this constitu- 

 tion constitutes the main portion of this chapter, which 

 closes with the statement of some of the more important 

 and immediate problems of solar physics. 



The usually received theory of the constitution of the 

 photosphere is given (p. 290) and the first authoritative 

 criticism of the recently proposed theory of Dr. Hastings 

 is given on pp. 291-294. It seems to the writer, however, 

 that Prof. Young, in urging as an obvious objection to 

 this theory, that whatever is precipitated at a lower tem- 

 perature than is the photosphere element must increase 

 the depth of the photosphere, has overlooked an essen- 

 tial point of the argument. The photosphere substance 

 is supposed to have a much higher vaporization tempera- 

 ture than those of other elements, e. g. iron, therefore 

 any precipitated iron belongs, not to the photosphere, but 

 to the over-lying "smoke" envelope 1 



This chapter closes the work proper of which we have 

 been able to give but the barest outline. Its chief char- 

 acteristics seem to the writer to be : perfectly clear state- 

 ments of the facts of observation and what is far more 

 valuable, of the theories to be considered. These are 

 made definite by every way possible — by lucid statements 

 and by diagrammatic figures ; candid discussion of these 

 facts and theories in the light of the best information now 

 attainable; and lastly the drawing of the most certain 

 conclusions which are possible from the data, taking care 

 in each case to give a proper idea of the degree of cer- 

 tainty which our ptesent knowledge allows. 



These are high excellences and make the book a most 

 important one. In pointing them out the writer has done 

 no more than any reader can do for himself. 



Edward S. Holden. 



M. Cochery intends to spend the surplus of the Elec- 

 trical Exhibition, which is said to exceed 16,000/., in estab- 

 lishing a research laboratory for electricity. 



PROFESSOR Haeckei. is at present in Ceylon, where he 

 is to stay for three months making a scientific exploration 

 of the island. 



