l62 



NA rURE 



[December 17, 1891 



falling again, the wind had increased, and the sea was high. 

 The barometer continued falling, and the gale rapidly developed 

 its full strength. From early morning of the i6th, for nearly 

 twenty- four hours, it blew a hurricane, and the catastrophes 

 commenced with the loss of the Eber. 



Any attempted interpretation of facts so meagre must neces- 

 sarily be in a great measure speculative. We have given that 

 of Mr. ilayden, and others have been suggested. One, that of 

 Lieutenant Wiizel, is to the effect that the storm of the i6th was 

 distinct from that of the previous day, and originated over 

 Savaii (the island to the west of Upolu, in which is the harbour 

 of Apia). Another, by Mr. Button, is that the storm of the 

 15th, after approaching the Samoan Islands on a south-we>t 

 track, recurved to west and north-west, and durin^j the following 

 night again recurved sharply, describing a loop north of Savaii, 

 and then returning towards Upolu, whence it moved southwards 

 and south eastwards. Our own interpretation is somewhat 

 different from any of these, and seems to be more in accordance 

 with the habits of tropical cyclones, the movements of which are 

 by no means so erratic as that implied by Mr. Button's hypo- 

 thesis, while it does not involve the extremely and, we think, 

 improbably sharp recurvature suggested by Mr. Hayden, nor 

 the equally improbal)le generation of a second vortex cnly one 

 day in the rear of the storm of the 15th, as supposed by 

 Lieutenant Witzel. None of these explanations seem to take 

 account of the circumstances that attend the formation of tropical 

 cyclones, which, as we have elsewhere pointed out, differ in 

 many respects from the storms of the temperate zone. 



It is evident from [the considerable and steady fall of the 

 barometer at Apia from March 12 to 15, that the Samoan 

 Islands lay withm the area of disturbance in which the storm 

 was generated, and that the formation of the vortex was simply 

 the concentration of this disturbance, which probably took place 

 nearer to Apia than is suppo.-ed by Mr. Hayden, but still at 

 such a distance that the first effect of the concentration— viz. a 

 slight rise of the barometer in the area immediately around, and 

 especially on the polar side— was felt at the Samoan Islands. If, 

 then, as seems probable, the vortex was not formed until the 

 afternoon of the 15th, this, in conjunction with the ordinary 

 diurnal rise between 4 and 10 p.m., would account for the slight 

 rise observed at Apia on the latter part of that day, and only the 

 second fall to a minimum on the i6th was due to the actual 

 passage of the cyclone. From the severity of the storm, as felt 

 at Apia harbour, it is clear that Upolu must have been traversed 

 by at least a portion of the inner vortex, but it could hardly 

 have been very close to the centre, seeing that the barometer 

 never fell to 29 inches; and therefore the long duration of the 

 hurricane (24 hours) can only be explained by the very slow rate 

 at which the storm was then travelling. This slow rate of pro- 

 gression strengthens the probability that it had not proceeded 

 far from its birthplace, since, as a rule, tropical cyclones move 

 forward slowly at first, and only gradually acquire greater speed 

 of translation. It also strengthens the inference that it had 

 originated not very far to the north or north-east of Upolu. 



This explanation, as already remarked, can only be regarded 

 as tentative, but it seems at least worthy of consideration by 

 those who may have fuller data at hand. H. F. B. 



UNIVERSITY AND EDUCA TIONAL 

 INTELLIGENCE. 



Cambridge. — The Sheepshanks Astronomical Exibition has 

 been awarded to P. H. Cowell, Scholar of Trinity College. 



A memorial signed by 107 members of the Senate is published 

 by the Vice-Chancellor : it expresses the opinion that "the 

 whole question of degrees in science should be considered by 

 the University." Among the signatures are some of those who 

 took the Greek as well as some who took the anti-Greek side in 

 the recent controversy. 



In view of the fall in the aggregate of the Colleges the 

 Council of the Senate propose to obtain powers for deferring the 

 next increment of the College contribution to the University 

 from 1893 to 1895, and the following increment (from ^25,000 

 to ;f 30,000) for seven years further— namely, to 1903. 



Sir George Gabriel Stokes and Prof. Macalister, M.B., 

 are among the delegates appointed to represent the University 

 at the Bublin Tercentenary Festival next year. 



Mr. E. W. Hobson, of Christ's College, is approved as Beputy 



NO. II 55, VOL. 45] 



for the Lowndean Professor of Astronomy for the Lent and 

 Easter Terms. 



We regret to hear that Prof. Adams's health does not yet 

 allow him to resume his duties. 



SOCIETIES AND ACADEMIES. 



LuNI>ON. 



Royal Society, November 19. — " The Thermal Emissivity 

 of Thin Wires in Air." By W. E. Ayrton, F.K.S., and H. 



Kilgour. 



In 1884 it was observed experimentally that whereas the 

 electric current required to maintain a thick wire of given 

 material, under given conditions, at a given temperature was 

 approximately proportional to the diameter of the wire raised 

 to the power three halves, the current was more nearly pro- 

 portional to the first power of the diameter if the wire were thin. 

 When this difference in the behaviour of a thick and thin wire 

 was first noticed, it was regarded as being quite unexpected. 

 But, as pointed out by one of us in the course of a discussion at 

 a meeting of the Royal Society, the unexpected characier of the 

 result was due to people having assumed that the loss of heat 

 from radiation and convection per square centimetre <'f surface 

 per i'^ excess temperature was a constant, and independent of the 

 size and shape of the cooling body. 



The very valuable investigations that have been made on 

 emissivity by Mr. Macfarlane, Prof. Tait, Mr. Crookes, Mr. 

 J. T. Bottomley, and by Mr. Schleiermacher, had for their 

 object the determination of the variation of the emissivity with 

 changes of the surface and with change in the density of the gas 

 surrounding the cooling body, but it was not part of these 

 investigations to deteimine the change in the emissivity that is 

 produced by change in the shape and size of the cooling body. 

 Indeed, so little has been the attention devo;ed to the very large 

 change that can be brought about in the value of the emissivity 

 by simply changing the dimensions of the cooling body, that in 

 Prof. Everett's very valuable hook of " Units and Physical Con- 

 stants " the absolute results obiained by Mr. Macfarlane are given 

 as the " results of experiments on the loss of heat from blackened 

 and polished copper in air at atmospheric pressure," and no 

 reference is made either to the shape or to the size of the cooling 

 body. 



YNi.vember 19, 1891. — Since this paper was sent in to the 

 Royal Society a new edition of this book has appeared, and, in 

 consequence of a suggestion made to Prof Everett, the word 

 "balls" has been added after the word "copper" in this new 

 edition, as well as the following paragraph : — 



" Inflttence of Size. — According to Prof Ayrton, who quotes 

 a table in 'Box on Heat,' the coefficient of emission increases 

 as the size of the emitting body diminishes, and for a blackened 

 sphere of radius r centims. may be stated 



•0004928 -f :°o°36o9. 

 r 



The value of r in Macfarlane's experiments was 2."] 



The laws which govern the Io>s of heat from very thin cylin- 

 drical conductors have not only considerable scientific interest in 

 showing how the shape of a body affects the convection currents, 

 but they are of especial importance to the electrical engineer in 

 connection with glow lamps, hot-wire voltmeters, fuses, &c. We 

 therefore thought it desirable to ascertain the way in which the 

 law of cooling for thick wires, which involved the diameter raised 

 to the power three halves, passed into the law for the cooling of 

 thin wires, involving only the first power of the diameter. For 

 this object, the investigation described in the paper was com- 

 menced at the beginning of 1888, and the emissivity was 

 measured of nine platinum wires, having the diameters of I "2, 

 2"o, 2"9, 4"o, 60, 81, 93, 1 1 "I, and 14 mils, or thousandths 

 of an inch. 



Suspecting that some of the published results on the currents 

 required to fuse wires had been much influenced by the cooling 

 action of the blocks to which the ends of the wires were attached, 

 we started by making a calculation of the length necessary to 

 give to our wires, so that the loss of heat by conduction should 

 not introduce any important error into the determination of the 

 emissivity. To do this it was necessary to calculate the dis- 

 tribution of temperature along a wire through which a steady 

 current was flowing, and from which heat was lost by radiation, 



