October 6, 1892] 



NA TURE 



541 



tion of reading the account of work which it is impossible for 

 the student to repeat for himself, the methods adopted are quickly 

 understood and easily remembered, because the general methods 

 of analysis and synthesis have, in an easy forta, not only been 

 used, but discovered l>y the student himself. 



This method of course breaks down where an elaborate ex- 

 aminati<5h syllabus is imposed upon the beginner from the 

 outset, and even where this is not the case, every teacher must 

 adapt the method to his own conditions, only and always keep- 

 ing the fundamental principle in view. 



For the beginner in Chemistry whether he is later to specialise 

 in this subject or not, experience has convinced me that the 

 teaching of facts must give way to the teaching of method if a 

 sound basis is to be laid in chemical science, whilst the subject 

 opens the whole question of the value of Chemistry teaching 

 from the educational point of view. Grack Heath. 



The Temperature of the Human Body. 



There is a problem partly physiological and partly physical 

 which I shall be grateful if any reader of Nature can throw 

 light upon. 



1. I'he physiological. — I am assured by medical opinion in 

 which I have confidence that the temperature of the human 

 body is invariable from pole to equator of the earth. The 

 question I want to ask, assuming this to be true, is this : What is 

 the action in the body which exactly and everywhere counter- 

 balances the radiation and conduction of heal in the one case 

 from the body and in the other to the body? I thought at first 

 that perspiration might have something to do with it, but my 

 medical authority assures me that at the equator a man who 

 perspires freely has exactly the same tempeiature as one that 

 perspires little, although the former will be in good and the 

 latter in bad health. 



2. The physical. — Treating the animal as a heat engine, one 

 is apt to think of the source of heat as the qnimal heat engen- 

 dered by the combustion going on in his frame, and the re- 

 frigerator as the surrounding air at lower temperature — in the 

 experience of most of us. The animal then does work at the 

 expense of this heat during its transfer from source to re- 

 frigerator, as in an ordinary engine. On the other hand, the 

 animal in equatorial regions must, if ihe physiological statement 

 above be a fact, be often the coldest of surrounding bodies. 

 Does he also do work at the expense of the heat of combustion 

 in his body, and if so is this vital action an exception to the 

 .second law of thermodynamics ? If not, doe-; he do work at the 

 expense of the heat which is conducted into his body from hotter 

 surrounding bodies, which heat, when he is doing no external 

 work, still does not raise the temperature of his body ? 



Rugby. L. CuMMiNG. 



Comet n. 1892 (Denning, March i8). 

 This comet is still a tolerably easy object in my lo-inch re- 

 flectt)r and will doubtless continue to be visible during the 

 greater part of the ensuing winter. It is now approaching the 

 earth, and its brightness is increasing slightly. During the next 

 two months it will traverse Orion. 



I observed the comet on September 30, when it was in the 

 same field as the 6th mag. star Piazzi VI. i44(Lalande, 12546). 

 By differential observations with that star I found the place of 

 the comet to be 



G.M.T. a. h. 



h. m. h. m. s. o , 



1892, Sept. 30 ... 12 50 ... 6 25 51 ... +14 II. 



The theoretical brightness, as given in Schorr's ephemeris, 

 was o"62, but to my eye the comet seemed quite as plain as in 

 March last. The nucleus was, perhaps, not so distinct, but the 

 surrounding nebulosity appeared to be more extended than on 

 previous occasions. 



The comet will be close to ^Orionis (the southernmost star in 

 the belt) about November 14, and passes very near 3 Orionis 

 (Rigel) on November 30. W. F. Denning. 



Bristol, October 2. 



Cirro-stratus. 

 A rather pel feet example of one variety of this cloud was 

 seen here in the afternoon of September 27. A rapid fall of the 



NO. 1197. VOL. 46] 



barometer until 5 a.m., accompanied by a high wind, had been- 

 followed by a steady rise, the wind moderating some hours 

 later. At 2 p.ni., with a westerly light air, the sheet of cirro- 

 stratus which overspread the sky appeared in the form of a 

 series of very perfect undulations, stretching nearly north and 

 south. These were about fourteen m number, crowded together 

 towards the east. The lower surface of the sheet was sharply 

 defined, and could be followed with ease in its successive rise 

 and fall. The cloud- filaments could be also traced, preserving 

 their perpendicularity to the wave-fronts and conforming to the 

 undulations of the lower surface with a closeness which I had 

 not before observed, although sheets of cirro-stratus are common 

 here. The whole system was drifting slowly to the east. 



J. Porter. 

 Crawford Observatory, Queen's College, Cork. 



A New Habitat for Cladonema. 



Will you kindly allow me through your columns to note a 

 habitat for this genus not given in Allman or Hincks. Several 

 weeks ago I received some sponge from Mr. Sinel, of Jersey, 

 and on examining it with a hand-lens detected four polypites of 

 Cladonema, one, at least, of which is still alive. 



Henry Scherren. 



5 Osborne Road, Stroud Green, N. 



TO DRAW A ME RCA TOR CHART ON ONE 

 SHEET REPRESENTING THE WHOLE OF 

 ANY COMPLEXLY CONTINUOUS CLOSED 

 SURFACE. 



IF a solid is not pierced by any perforation, its surface 

 is called simply continuous, however complicated its 

 shape may be. If a solid has one or more perforations, 

 or tunnels,^ its whole bounding surface is called " com- 

 plexly continuous"; duplexly when these is only one 

 perforation ; («-f i)-plexly when there are n perforations. 

 The whole surface of a group of n anchor-rings (or 

 " toroids '■) cemented together in any relative positions 

 is a convenient and easily understood type of an («+ 1)- 

 plexly continuous closed surface. 



Let the diagram represent a quadruplexly continuous 

 closed surface made of very thin sheet metal, uniform as 

 to thickness and homogeneous as to quality throughout. 

 To prepare for making a Mercator chart of it, cut it open 

 between perforations C and B, B and A, A and outer 



2 I 



space, in the manner indicated at => =, and ± . Apply 



3 4 



in6nitely conductive borders to the two lips separated 

 by the cut at ±, and apply the electrodes of a voltaic 



battery to these borders. By aid of movable electrodes 

 of a voltmeter trace, on the metallic surface, and a very 

 large number («- I, of equidifferent equipotential closed 

 curves between the + and - borders. Divide any one of 

 these equipotentials - into parts each equal to the 



1 A "hole" may mean a deep hollow, uot through with two open ends. 

 The word "tunnel" is inappropriate for the aperture of an anchor ring. 

 Neither " hole " nor "tunnel" being unexceptionally available, I am com- 

 pelled to use the longer word "perforation." 



- Two sentences of my previous article ("Generalisation of Mercator's 

 Projection ") in § 3, and in last paragraph but one, are manifestly wTong, 

 and must be corrected to agree with the rule given for dividing into infini- 

 tesimal sriuares. in the present text. 



