April 26, 1877] 



NATURE 



547 



I 



of ornithology we welcome Mr. Vennor, and only trust 

 that many years will not elapse before he gives us a 

 second instalment on the birds of Canada. 



OUR BOOK SHELF 



The Use pf the Spectroscope in its Application to Scienfific 



and Practical Medicine. By Emil Rosenberg, M.„D. 



(New York : Putnam, 1876.) 

 This is an essay on the use of the spectroscope which 

 obtained the Stevens triennial prize for 1876, awarded by 

 the College of Physicians and Surgeons. 



It treats mainly of the absorption spectra of blood in 

 its normal state and after being acted upon by other sub- 

 stances. The first chapter gives a very short account of 

 the optics of the spectroscope, which the author does not 

 pretend to treat fully ; then follows a short notice of the 

 emission spectra of the metals. The absorption bands of 

 oxyhsemoglobin (scarlet cruorine) and their change to the 

 one reduction band of haemoglobin (purple cruorine) by 

 the abstraction of oxygen, discovered by Prof. Stokes, 

 then comes in for recognition. The remainder of the 

 book is chiefly on the absorption spectrum of blood with 

 reference to forensic medicine and its spectrum after the 

 introduction of foreign matters and gases. 



It appears from the numerous references that the author 

 has compiled this essay from books and papers rather 

 than from observation, and the authors referred to are 

 with few exceptions Germans. We think the book is well 

 suited for" the perusal and reference of the medical pro- 

 fession and others taking up this special subjfect. 



Joicrney in the Caucasus^ Persia, and Turkey-in-Asia. 

 By Lieut. Baron Max von Thielmann. Translated by 

 Charles Heneage, F.R.G.S. Two vols. Map and 

 Woodcuts. (London, Murray). 

 Baron Thielmann's journey, which was made in the 

 year 1872, embraced all the Caucasian region, 'much of 

 the western shore of the Caspian Sea, with the long 

 stretch of country between Tabrez, Hillah, and Beyrout. 

 Though this is a region about which a good deal has 

 been written, the Baron's narrative will be found to con- 

 tain a considerable addition to our knowledge. His 

 observations on the people and the antiquities of the 

 countries traversed are especially valuable, while the 

 work contains as well much interesting topographical and 

 geographical information. The Baron is an exceedingly 

 pleasant travelling companion, and as Mr. Heneage has 

 made a thoroughly readable translation, the work will be 

 found of value both to the stay-at-home reader and as a 

 guide to the intending tourist. 



LETTERS TO THE EDITOR 



\The Editor does not liold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of rejected manuscripts. 

 No notice is taken of anonymous communications. 



The Editor urgently requests correspondents to keep their letters as 

 short as posiible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the apfarance even of com- 

 munications containing interesting and novel facts. ] 



Structure and Origin of Meteorites 



In the abstract of Mr. II. C. Sorby's lecture "On the Struc- 

 ture and Origin of Meteorites," given in ]Nature, vol. xv., 

 p. 495, in reference to the subject of glass globules observed by 

 the lecturer in certain meteorites, the condition in which glassy 

 particles given off by terrestrial volcanoes occur, is contrasted 

 with that produced artificially in furnace slag by the action of a 

 strong blast of hot air or steam. In the furnace slag " pear- 

 shaped globules, each having a long hair-like tail," are described 

 as being formed, whereas in the case of volcanoes the glassy 

 particles are said, when given off, to be immediately solidified 

 on entering the atmosphere, and to remain as mere fibres, as 

 Pele's hair, or more or less irregular laminae, like pumice dust. 



In fact, the formations in the two instances are closely similar. 

 In the crater of Kilauea, in the Island of Ilawai, wherever the 

 well-known Pele's hair is in process of formation, long-tailed 

 pear-shaped globules are formed in abundance, and a large pro- 

 portion of the "hairs" are to be found with larger or smaller 

 globules in connection with their ends. 



I saw the formation of Pele's hair in two places in the crater. 



In the one instance the formation occurred vA the margin ot 

 one of the small lakes of molten lava. The lake was inclosed 

 by a range of low cliflTs, against the bases of which the waves of 

 the extraordinarily fluid lava were constantly surging, being kept 

 in perpetual commotion by the violent discharge of gases from 

 beneath. The waves splashed up against the cliffs and spray 

 and large drops were thrown into the air, and on the leeward side 

 of the lake were driven by the wind over the top of the cliff so 

 as to fall on a level platform of rock which was even with its 

 summit. 



The platform appeared as if melted pitch had been splashed 

 out all over it, and was covered with small masses of pitch-like 

 looking lava. Those of the masses which had evidently com- 

 pletely solidified before reaching the platform in their fall were 

 pear-shaped, whilst in other cases where hardening had not 

 been complete, the elongate masses falling in the soft condition 

 had become flattentd into irregular shapes, which showed more 

 or less evident traces of the coiling of the masses as they fell. 



All the masses had tails, some short and spike-like, others long 

 and hair-like, and there was every gradation between stiff fine rods 

 of transparent lava and the perfectly elastic hair of which a handful 

 could readily be raked together with the fingers on the platform 

 in a very short time. 



In the other instance, the Pele's hair was reen by me around 

 one of the small hollow cones or lava fountains which are con- 

 stantly formed in the crater. The cone was not active at the 

 time I saw it. It was surrounded with the small lava masses 

 thrown out by it and forming a deposit closely similar to that 

 formed at the margin of the lake, except that numerous larger 

 lumps occurred amongst the smaller ones. 



Very striking objects in the crater are large bubbles which 

 have been formed in the lava when molten by the escaping gases. 

 The surfaces of the bubbles are composed of extremely thin 

 transparent laminje, which look just like thin green bottle glass. 

 Such bubbles are encountered at almost every step on the floor 

 of superficially solidified lava, on which the visitor walks in the 

 crater. 



A remarkable peculiarity of the Hawaian lava is its ex- 

 treme fluidity when in the molten condition. This property 

 has brought about the unusual form of the great mountains of 

 the island composed of it, which have so gradual a slope that 

 the observer can hardly credit their great height when viewing 

 them from the sea. II. N. Moselev 



Exeter College, Oxford 



On the Simplest Continuous Manifoldness of Two 

 Dimensions and of Finite Extent 



It could hardly fail to be instructive if Mr. Frankland would 

 explain the following obvious paradox in his theory (Nature, 

 vol. XV., p. 515). Let two •' straight lines " xox', lol', make 

 an angle XOL other than a right angle, and consider the shortest 

 line PN from a moving point P in ll' to xx' ; from the assump- 

 tions, this is a "straight line" perpendicular to xx'. As P 

 moves from o along OL, it will by and by, according to the 

 theory, be at l' ; that is, on the other side of xx', if our 

 "straight lines" are "of the same shape all along." Now, to 

 put it algebraically, how does the perpendicular come to change 

 sign ? It does not pass through infinity, for the manifoldness is of 

 finite extent : it does not vanish except when p is at o ; and 

 though it is conceivable in itself that N should travel to a maxi- 

 mum distance along ox and come back again while p moves on, 

 yet this contradicts our principal assumption, for each perpen- 

 dicular will then have two points in common with ll'. Is a 

 door of escape to be found through any interpretation of " con- 

 tinuous"? Or, while "there is nothing self-contradictory in 

 the definition," is there something in it contradictory of the 

 superposition-principle by means of which its consequences are 

 worked out ? 



The theory is partly exemplified upon the surface of revolution 

 got by bending a hemisphere till it closes up. Correspondence 

 is pretty close as to points in the equator and the simpler figures 

 symmetrical to it. C. J. Monro 



Hadley, Barnet 



