May 26, 1 881] 



NATURE 



ness. The eftect of contact in producing or maintaining 

 difference of potentials would be perceived by a difference 

 in electric brilliancy, and this difference would vary with 

 each re-arrangement of the objects. Every movement of 

 our body, each touch of our hand, and the very friction of 

 our clothes, would cause a play of effects analogous to 

 those of light and shadow on the eye, while more highly 

 electrified matter would bring into prominence by induc- 

 tion electrical differences between surrounding bodies. 

 This speculation, however fanciful, helps us to conceive 

 the omnipresence of electricity; and since the mechanical 

 conditions required to excite sensation are fulfilled in the 

 electrical relations between bodies at different potential?, 

 there does not seem any very great boldness in suggesting 

 that some living things may have an clcctrostaiic sense so 

 far developed as to be of use to them""' (page 51). 



Altogether this little work forms a very suitable intro- 

 duction to its author's much more advanced and well- 

 known "Textbook of Electricity and Magnetism." 



The Natural History of the Cranes. A Monograph by 

 the late Edward Blyth. Greatly enlarged and reprmted 

 with numerous illustrations by W. B. Tegetmeier. 

 (Published for the Author, 1881.) 

 This is an excellent monograph of an exceedingly inte- 

 resting group of birds. On the arrival in 1 87 3 of a pair of 

 the beautiful white-najjed cranes of Japan in London 

 they were drawn by Mr. T. W. Wood for the /"/V/<^ news- 

 paper, and the late Edward Blyth took the opportunity of 

 publishing in the columns of that paper a monograph of 

 all the then known species of crane. At the suggestion of 

 Prof. A. Newton, Mr. Tegetmeier has republished these 

 notes, inserting however much new matter that eiiher 

 want of space had prevented Blyth from incorporating, 

 or that had come to hand since Blyth' s death. Thus we 

 have WoUey's graphic account of the nesting of the 

 common crane in Lapland, Dr. CuUen's account of the 

 nesting of the Demoiselle in Bulgaria, and even Col. 

 Prjevalsky's account of a new species found at Koko-nor. 

 Sixteen species, two belonging to the genus Balearica and 

 fourteen to the genus Grus, are described. Mr. Wood's 

 figures of Grus Uuciaiclien are reproduced. There is a 

 facsimile of the coloured figure of Grus nigricollis from 

 Col. Prjevalsky's " Birds of Mongolia" ; a spirited sketch 

 by Prof. W. H. Flower of flocks of Grus I'irgo on the 

 banks of the Nile ; some copies of studies of cranes from 

 Mr. Cutler^s beautifully-illustrated work on Japanese 

 ornament (charming studies) ; and a few woodcuts of 

 anatomical details. 



Cranes of one or more species are found everywhere, 

 with the exception of South America, the Malayan and 

 Papuan Archipelagos, and the scattered islands of the 

 Pacific. The common European species, celebrated in 

 all times for its migrations — 



" So steers the prudent crane 

 Her annual voyage, borne on winds ; the air 

 Floats as they pass, fann'd with inmumber'd plumes " — 



was at one time very numerous in the fenny districts of 

 England ; so possibly Milton knew the bird. The name 

 is quite wrongly applied to the heron in Scotland and 

 Ireland, while in America and .Australia the white egret 

 herons are also called cranes. Old yEsop's fable of the 

 stork being captured in the evil companionship of the 

 cranes, and being condemned to death for thus even 

 associating with notorious plunderers of grain, indicates 

 that he well enough knew the two kinds of birds ; far 

 better indeed, as Blyth truly remarks, than did that 

 renowned master of medireval painters, who commits the 

 curious zoological mistake of introducing cranes instead 

 of storks in his world-known cartoon of the Miraculous 

 Draught of Fishes. 



In common with many other gregarious birds, cranes 

 always place sentinels as a lookout, while the rest of the 



flock will trustfully repose ; and they like\Yise leave them 

 on the watch while on their marauding expeditions to 

 crops of grain. 



Zoological Atlas {Including Comparative Anatomy) 

 With practical directions and explanatory text for 

 the use of students. 231 coloured figures and dia- 

 grams. By D. McAlpine. \'ertebrata. (W. and 

 A. K. Johnston, 1881). 

 The object of this work is to help the student in the 

 examination and dissection of the leading types of animal 

 life. The author quotes Dr. Macalister's words, ''That 

 in a practical science such as zoology it is only by the 

 examination of specimens that any knowledge of the 

 science worth acquiring can be obtained, and the function 

 of a book is to assist in practical study." Bearing this in 

 mind, he has here triecl to assist the student by giving 

 descriptions and drawings of one selected specimen from 

 each group of the vertebrates. The skate and cod have 

 been chosen to represent the cartilaginous and bony 

 fishes respectively ; the salamander to represent the tailed 

 amphibia ; the tortoise to represent the reptiles ; and the 

 pigeon and rabbit to represent the birds and mammals. 

 The various systems are well represented, with the excep- 

 tion of the muscular system, which perhaps has been 

 wisely overlooked. There can be no doubt but that this 

 Atlas will form an important addition to the working 

 student's books. It should remove many elementar>' 

 difficulties from his path. 



LETTERS TO THE EDITOR 

 [The Editor does not hold h tinsel/ responsible for opinions expressed 

 by his correspondents. Neither ean he undertake to return, 

 or to correspond -,vilh the vjritcrs of, rejected inanuscrifts. 

 No notice is taken of anonymous communications. 

 [ The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible olheniise to ensure the appearance even 

 of communications containing interesting and novel facts.} 



Dr. Carnelley's Experiment with Mercuric Chloride 

 I WAS a little surpri>ed to notice from a paragraph in I'rof. 

 McLeod's letter in Nature, vol. xxiv. p. 28, that he had been 

 unable to repeat Dr. Carnelley's experiment w itb mercuric 

 chloride. Immediately after the publication of my former letter, 

 it was remarked to me, that although I had shown hot ice to be 

 an imposible commodity, perhaps Dr. Carnelley's assertion 

 of the txitence of solid mercuric chloride above its boiling point 

 might still hold. I therefore repeated this experiment, and after 

 overcoming a few preliminary tlifficulties, obtained a result 

 similar to that with ice. The difficulties were these : — After 

 solidifying a cylinder of mercuric chloride round the thermometer 

 (to which it adhered at fir-t), on heatinij, the mtrcuric chloride 

 soon became detached and fell from the thermometer. It had 

 therefore to be sustained in position round thejthermometer, by a 

 stout iron or copper wire. Another difficulty arose from the fact 

 that the mercuric chloride soon became deeply pitted and fissured, 

 so much so, that the thermometer was sometimes seen through 

 holes a quarter of an inch deep. This pitting went on till the 

 mercuric chloride cylinder, though not much reduced in diameter, 

 became a mere network, the thermometer being visible in many 

 places. The erosion seemed to take i lace m .re quickly next 

 the bulb ; making the holes in the cylinder wiriest ::t the interior. 

 Another difficulty lay in the high temperature causing, as I'rof. 

 McLeod noticed, the rupture of the thermc meter thread ; but by 

 using a very good thermometer, and keeping it as nearly vertical 

 as was convenient, this was entirely obviated. A large condenser 

 is not required, and I only used a piece cf combustion tuling 

 fully an inch in diameter and about twenty inches long, the 

 thermometer with the cylinder of mercuric chloride being inserted 

 at one end, and a tube connected with a Sprengel pump at the 

 other. The re.-ults obtained are as fellows :— Melting point of 

 mercuric chloride, 271° (uncorr.) ; boiling point, 291° (uncorr.). 

 The pressure was now reduced to 400 mm., and the tube heated 

 until the temperature was constant, the pressure again reduced, 

 another reading taken, and so on until a vacuum was reached, or 

 the cylinder had become too porous to give correct readings. 



