5 o8 



NA TURE 



[March 29, 1906 



enhanced lines. Little is said about this chemical 

 classification by Miss Gierke, and nothing in its 

 favour, yet it represents the conclusions of a lifetime 

 devoted to the study of spectra in the laboratory and 

 observatory, and abundant material relating to il 

 appears in the Proceedings of the Royal Society. 

 Anyone unfamiliar with this material who reads what 

 Miss Gierke has to say upon the temperatures of the 

 star-, and the interpretation of stellar spectra would 

 have an inadequate idea of the results of systematic 

 studies of these subjects, or of the existence of sub- 

 stantial ground of appeal against her verdict. 



An instance of an incomplete statement that tends 

 to mislead the reader is afforded by the note on Sir 

 William and Lady Huggins's experiments on the be- 

 haviour of the H and K lines of the spectrum of 

 calcium (Roy. Soc, June 17, 1S97). By reducing the 

 density of calcium vapour the lines H and K were 

 obtained alone, and it was concluded that the various 

 appearances of calcium lines in celestial bodies were 

 due to the different states of density of the gases from 

 which the lines were emitted or absorbed, and not to 

 degrees of dissociation. The H and K lines in the 

 solar spectrum are considered to prove the existence of 

 " the metal calcium in a highly rarefied state "; and 

 upon this evidence, referring to the condition of 

 this element, Miss Gierke remarks : — " The hypo- 

 thesis of its dissociation in the sun thus remains 

 unverified." As a matter of logic, the experiments 

 only prove that the H and K lines of calcium 

 are spectroscopically persistent, and were able to 

 survive (as might have been expected) conditions 

 which effaced weaker lines in the spectrum of the 

 element. Because brachiopods belonging to the genus 

 Lingula are found in the sea at the present day as 

 they were in Palaeozoic ages, while many other forms 

 that were contemporary have disappeared, we do not 

 conclude that organic evolution is impossible, but only 

 that the organism represents a type which persists in 

 spite of changes of conditions. In the same way the 

 continued existence of the H and K lines affords no 

 evidence whatever against the view that there are 

 different molecular groupings of calcium at different 

 temperatures. By reducing the density of the calcium 

 vapour, Sir William and Lady Huggins reduced the 

 quantity acted upon ; so the dissociated condition re- 

 presented by the appearance of H and K alone was 

 reached sooner. Similar experiments were made by 

 Sir Norman Lockyer in 1879, and the conclusion 

 arrived at was that a reduction in the quantity of a 

 substance generally simplifies the spectrum. " In all 

 probabilitv the effects hitherto ascribed to quantity 

 have been due to the presence of the molecular group- 

 ings of greater complexity. The more there is to 

 dissociate, the mure time is required to run through 

 the series, and the better the first stages are seen 

 (Roy. Soc. Proc, vol. xxx., p. 26). 



It will be seen, then lore, that the principal point 

 of Sir William and Lady Huggins' experiment on 

 calcium vapour at different densities was the subject 

 of laboratory experiments more than twenty years 

 earlier, and that their conclusion, though it is men- 

 tioned by Miss Clerke without reservation or reference 

 NO. 1900, VOL. 7$} 



to previous investigations, is not a safe one to apply 

 to the consideration of the condition of calcium in 

 the sun or stars as indicated by spectroscopic appear- 

 ance. Moreover, if the changes of the calcium spec- 

 trum are interpreted as effects of tenuity, the similar 

 spectral variations of magnesium and iron ought to 

 admit of a like explanation, whereas there is good 

 evidence that they are due to constitutional changes 

 brought about by thermal or electric action. 



Many other debatable matters are dealt with by 

 Miss Clerke in a manner which suggests that the 

 last word has been said upon them when she is really 

 only presenting one side of a case. It may be assumed 

 that, like a good advocate, she is as familiar with the 

 defendant's case as she is with the plaintiff's, but the 

 real strength of the evidence opposed to the views she 

 adopts could only be shown by the disciple of another 

 school of spectroscopy ; and a small volume would be 

 required to plead this cause. No writer on astronomy 

 has a more facile pen than has Miss Clerke, and we 

 can forgive the occasional florid style when we re- 

 member the vast amount of reading and careful 

 analysis involved in the preparation of a volume of 

 this kind. The work is so good that every student 

 of astronomical physics must be familiar with it, and 

 every astronomical library must include it. Because 

 of its essential qualities it is to be regretted that a 

 broad view has not been taken of all contributions to 

 the subject made by competent investigators ; for by 

 neglecting such aspects as have been referred to in 

 the foregoing paragraphs an incomplete story is pre- 

 sented of the meaning and mysteries of sidereal 

 development revealed by spectroscopic research. 



R. A. Gregory. 



BRITISH A^CIDIANS. 

 The Britisli Tunicata: a>i Unfinished Monogtaph. 

 By the late Joshua Alder and the late Albany 

 Hancock. Edited by John Hopkinson, with a His- 

 tory of the Work by the Rev. A. M. Norman, 

 F.R.S., &c. Vol. i. Pp. xvi+146 + xx plates. 

 (London : Printed for the Ray Society, 1905.) Price 

 I2X. 6d. net. 



THERE are probably few precedents for the publi- 

 cation of an unfinished biological monograph 

 thirty years after the authors penned their last re- 

 marks, especially of a monograph dealing with a 

 group which has been the object of much detailed 

 investigation by other hands in the interval. The 

 chequered history of the present work is briefly, but 

 sympathetically, told by Canon Norman, from whose 

 preface the following paragraph may be extracted : — 



" Though so many years have elapsed, the value of 

 this Monograph is great, since (ist) it contains full 

 descriptions with illustrations of the Tunicata of our 

 fauna as known up to the time of the death of the 

 authors; (2nd) because many of the new species had 

 been only briefly diagnosed, and the fuller descrip- 

 tions and figures of these which are now given will 

 enable them to be better known and understood ; and 

 (3rd) it is especially desirable that the full account of 

 Hancock's investigations should be published together 

 with a portion of his beautiful drawings." 



