NA TURE 



[NoVEMBEK 14, 19OI 



characteristic fossils, the leading zonal forms— O/enclltis, 

 Paradoxides, Otcnus and Dictyoiieiiia- -being the only 

 fossils noted from the Cambrian system. In dealing 

 with Ordovician and Sikirian strata the graptolite zones 

 receive particular attention, and other zonal fossils are 

 mentioned. The full stratigraphical details relating to 

 these systems make one feel that scant justice is done to 

 the Devonian ; but as a matter of fact our knowledge of 

 that system is far less precise. Here, as occasionally 

 elsewhere, a column for Continental divisions is given. 

 In the Lower Carboniferous, Mr. Hobson starts with the 

 Devon succession and places the Lower Culm Measures 

 with the Coddon Hill Beds on the horizon of the Lower 

 Limestone Shales, whereas their characteristic Posi- 

 donomya and Goniatitrs indicate an horizon equivalent 

 to the Upper Carboniferous Limestone or Voredale Series. 

 He has not, however, ventured to indicate zones in the 

 Carboniferous, although materials have been gathered m 

 the neighbourhood of Bristol as well as in northern 

 counties, to which reference is made in the preface. Here 

 and there we would suggest a greater uniformity m 

 method : for instance, the Ammonite zones of the Lias 

 are noted under the names ^Egoceras, &c. : those of the 

 Inferior t)olite are noted as Parkinsoni zone, iS;c. ; and 

 those of the Cretaceous rocks as ADimouiles litiitus, &c. 

 The most difficult correlation is, doubtless, that of the 

 Pleistocene, and here the student may well pause, for the 

 " Upper Boulder Clay " of different areas is not to be 

 regarded as contemporaneous. Indeed, the compiler in 

 his preface remarks that " strata named on correspond- 

 ing horizontal lines cannot, in some cases, be considered 

 to be of corresponding age " ; and the student will do well 

 to bear this in mind. 



The work is issued as one of the museum handbooks 

 of the Manchester Museum, Owens College. It cannot 

 fail to be of great service for reference to geologists in 

 general. It bears evidence of the most painstaking care 

 and of wide research up to the date of publication ; and 

 we feel confident that the labour will be appreciated. 



Die Partielhn Differential-gleiihungen der mai/iema- 

 iischen Physik. By Heinrich Weber, based on 

 Riemann's lectures. Vol. ii. Pp. 527. (Brunswick: 

 Fried. Vieweg and Son, 1901.) 



In reviewing the first volume of this book (N.^ture, 

 vol. Ixiii. p. 390) it was pointed out that owing to the great 

 advances in mathematical physics which have taken 

 place in the forty years since Riemann's time. Prof. 

 Weber had found it necessary, instead of merely issuing 

 a revised edition of the well-known " Partielle Differential- 

 gleichungen," to v/rite practically an entirely new book. 

 The present volume, which is written much on the same 

 general lines as the first, is divided into five parts. 

 The first contains the more important properties of 

 hypergeometric series and their application to the theory 

 of linear differential equations. The second part, dealing 

 with conduction of heat, is much after the lines of 

 Riemann's original treatment, and treats mainly of con- 

 duction in one dimension and conduction in a sphere. 

 The third part is devoted to theory of elasticity and 

 vibrations, the torsion problem being included in the 

 former subject, and vibrations of strings and membranes 

 in the latter. Electrical oscillations come next in order, 

 and the last part consists of hydrodynamics and pro- 

 pagation of plane and spherical sound-waves, including 

 Riemann's own theory of sound-waves of finite amplitude. 

 Seeing that a whole volume might be written on any 

 one of these branches of mathematical physics and still 

 leave many interesting points untouched, the treatment 

 in the present book is necessarily but fragmentary in 

 character, but Prof Weber is to be congratulated on the 

 number of points which he has been able to touch in the 

 limited space of about 500 pages. At the end is an 

 index to both volumes. (i. H. B. 



NO. 1672, VOL. 65] 



LETTERS TO THE EDITOR. 

 [ The Ediloi- doe: not hold himself respoiisilde for opinions ex- 

 pres'!ed by his correspondents. Neither can he undertake 

 to return, or to <o> respond with the writers of, rejei.ei 

 mantisciipts intended for this or any other part of Nature. 

 No notice is taken of anonvmous communications.'^ 



The Total Solar Eclipse of September 9, 1904, 



As inquiries have already been addressed to me as to the 

 practicability of observing this eclipse, which passes across the 

 Pacific Ocean (see " Nautical Almanac," 1904, pp. 4S7-490), 

 perhaps I may be allowed, thus early, to communicate, through 

 your instrumentality, the information I have collected on the 

 subject. 



The Walker Islands, which appear on some maps of the 

 locality in the position 149' W., 4° N., would have been, if they 

 existed, very favourably situated for the observation of the 

 eclipse. But recent surveys have shown conclusively that they 

 do not exist. 



Kingman, or Caldew, Reef, 162' W., 6° N., is also favourably 

 situated, but is stated in the Admiralty Sailing Directions to be 

 partially dry at low waler only. 



Palmyra Island is placed by the most recent survey in the 

 position 162" 6' W., 5° 52' N., and is thus a little loo far soulh> 

 to be available. Proceeding westwards, the next group of 

 islands encountered is the Marshall Islands. But even the 

 most easterly of the group on the track of the eclipse — Aur — is 

 loo far west for our purpose, as the middle of the eclipse occurs 

 there shortly after sunrise. 



It appears that there is no island conveniently placed for the 



observation of this eclipse, and astronomers must wait for the 



total eclipse of the following August, which will afford ample 



opportunity for observation in Canada, Spain and North Africa. 



A. >I. \V. UOWN-ING. 



The Dilution of Acetylene for Heating Purposes. 



YOLT have been good enough on one or two previous occa- 

 sions to give me a few lines in your columns on questions con- 

 nected with acetylene for heating, and as this use of the gas is 

 extending and will undoubtedly have a much wider extension 

 in the near future, perhaps you will renew your courtesy in this 

 matter. 



In country places for domestic and laboratory purposes, more 

 especially with the advance of electricity and decline of coal gas 

 for lighting, the field for acetylene for heating is very large and 

 has so far met with strangely little consideration. The com- 

 bustion of a gas containing 92 per cent, of carbon successfully 

 in a Bunsen burner is not more easy than its combustion to 

 produce a trustworthy luminous flame. The chief difficulty 

 from which we suffer in the former matter is the relatively high 

 pressure under which the gas must be burnt. No one has yet 

 devised a Bunsen burner which will give a flame large enough 

 for ordinary working purposes under a pressure of less than six 

 inches of water, and even then luminosity is not entirely 

 banished, practically no margin being left for incorrect adjust- 

 ment of the burner. The pressure is objectionable, it puts the 

 gas fittings to a severe test in the matter of leakage, it is much 

 more than is required for lighting and has to lie specially ar- 

 ranged for in many generators, and in those of the automatic 

 class it involves more "after gas," necessitating larger storage 

 capacity. The fine orifice of the jet and the necessarily narrow 

 tube with its accompanying increased internal friction and the 

 large injecting power essential, all make high pressure a necessity. 

 That this luminosity trouble is partly a matter of temperature 

 can be easily shown by heating the tube of a non-luminous 

 Bunsen, or pouring water on to the tube of one showing 

 luminosity, the effect being very striking, and some improve- 

 ments on these lines have suggested themselves and are efficient 

 as far as they go. We want, however, to attack the root of the 

 matter and dilute our acetylene to begin with, and this dilution 

 would not be altogether objectionable from a lighting point of 

 view. Lighting burners at present generally inject some air 

 and can only themselves be regarded as on the verge of respect- 

 ability ; quite an absurdly small amount of benzene vapour is 

 .sufficient to put out of temper the lighting burners now on the 

 market. Such dilution would give them the margin for bad 

 usage which makes so much for success in practice, even though 

 wasteful in theory. 



