May lb, 1 872 J 



NATURE 



51 



pression above given, the unknown resistance R' can be 

 easily calculated ; but in order to facilitate the use of the 

 instrument, I have prepared a table which gives at a ghnce 

 the resistance due to any two observed volumes, the 

 volumes V governing the vertical, V the horizontal 

 columns, and the resistance being read off at the point of 

 intersection. At each point of intersection the resistance 

 is marked in black, and the corresponding temperature in 

 red ink. 



It now lemains only to be shown what is the relation 

 between the resistance and temperature in heating a 

 platinum wire. The researches of Dr. Matthiesen, who 

 has made the latest investigations on the effect of tempera- 

 ture upon electrical resistance, are restricted to the narrow 

 range of temperatures between 0° and 100" Centigrade, 

 nor do they comprise platinum. He adopted the follow- 

 ing general expression for the pure metals : — 



which, in determining the specific values of .i- and y for 

 each metal, gives a close agreement with observation be- 

 tween the narrow limits indicated, but is wholly inappli- 

 cable for temperatures exceeding 200' Centigrade, when 

 the value t- commences to predominate and to produce 

 absurd values for R^. 



It was necessary for my purpose to undertake a series 

 of elaborate experiments with a view of finding a ratio 

 of general application. Coils of thin wire, of platinum, 

 iron, copper, and some other metal?, were gradually 

 heated and cooled in metallic chambers containing the 

 bulbs of mercury thermometers, and for higher tempera- 

 tures of air thermometers, and the electrical resistances 

 were carefully noted. The progressive increase of elec- 

 trical resistance was thus compared directly with the in- 

 creasing volume of a permanent gas (carefully dried) 

 between the limits of zrro and 470' Centigrade, and a ratio 

 established which is represented by the formula — 



R. = aT=+/3T-fy, 



in which T signifies total temperature counting from the 

 absolute zero, and a, fi, and y specific; coefficients for each 

 metal. According to this formula the electrical resistance 

 is a constant at the absolute zero, and progresses in a 

 ratio represented graphically by a tipped-up parabola, 

 approaching more and more toward a uniform ratio at 

 elevated temperatures. Although the comparison with 

 the air thermometer could only be carried up to 470° C, 

 the general correctness of the ratio of increase just stated 

 has been verified by indirect means in measuring pro- 

 gressive heats, and by comparison with the platinum ball 

 pyrometer. 



It is important to mention here that great care must be 

 exercised in the selection of the platinum wire for tiie 

 measuring spiral, platinum wire having been met with 

 conducting only 47 times better than mercury at zero C, 

 and others conducting 8 2 times better than mercury, 

 although both samples had been supplied by the same 

 ■ eminent makers, Messrs. Johnson and Mathey. The ab- 

 normal electrical resistance of some platinum wire is due 

 chiefly to the admixture of iridium or other metals of the 

 same group, and it appears that the platinum prepared by 

 the old weiding process is purerand therefore better suited 

 for electrical purposes than the metal consolidated by 

 fusion in a DeviUe furnace. 



In conclusion, I shall show some working results of the 

 pyrometer in measuring by means of the same protected 

 coil a mixture of ice and water, boiling water, molten lead, 

 and the fire itself by which the lead is melted, the read- 

 ings produced being 2° C, 98^ C, 330^ C, and 860° C. re- 

 spectively. The latter temperature signified a cherry red 

 heat, as may be judged by the appearance of the tube 

 when withdrawn from the fire. The instrument which I 

 have had the honour to bring before you this evening has 



already received several useful applications. Through its 

 first application an important telegraph cable was saved 

 from destruction through spontaneous generation of heat. 

 Prof Bolzani, of Ka^an, has made some interesting appli- 

 cations of it for recording the temperature at elevated 

 points and at points below the eai ill's surface. Mr. Low- 

 thian Bell has used it in his wcll-kno^'n researches on 

 blast-furnace economy ; and at several ironworks pyro- 

 meter tubes are introduced into the heating stoves, and 

 permanently connected with the office, where the heat of 

 each stove can at all times be read off and recorded. 

 The!e and other applications are sufficiently self-evident, 

 if the soundness of the principles upon which I re'y is 

 conceded ; but I feel that the shoriness of time at my 

 command ha; hardly enabled me to do more than to pass 

 these in review, while endeavouring to demonstrate the 

 results obtained of recording the temperatures of distant 

 or inaccessible places, including furnace temperatures. 



NOrES 



The "Faraday lecture" of the Chetnicil .Society will lake 

 place on Thursday, May 30, at S o'clock, in the theatre of the 

 Royallns'itution, Albemarle Street. This lectureship, founded 

 in honour of the late Prof. Faraday, was inaugurated two years 

 since by a masterly address given by M. Dumas of Paris. Prof. 

 Cannizzaro of Palermo has consented to deliver the lecture this 

 yea", which will ba anticipated with much interest ; he has 

 chosen as his subj-oct "Considerations sur quehjues points de. 

 rEnseiynement theorique de la chimie." 



At tile maetinj; of the Royal Geograp!iical Society held on 

 Mondiy evening last, Sir Henry Ravvlinson said that the opinion 

 of the Council of the Socieiy was favourable to the authenticity 

 of the intelligence received by telegram respecting Dr. Living- 

 stone. They had every reason to expect that Dr. Livingstone 

 and Mr. Stanley would meet about the beginning of the year. 

 But if there had been aay discovery and relief, it was Dr. Living- 

 stone that had discovered and relieved Mr. Stanley, and not 

 Mr. Stanley who had discovered and relieved Dr. Livingstone ; 

 because Dr. Livingstone was in clover and Mr. Stanley was ab- 

 solutely destitute. They knew by the last account that Mr. 

 Stanley was without supplies, and he must have undergone 

 much difficulty in getting to Ujiji; whereas this place was the 

 head-quarters of Dr. Livingstone's supplies. He expected that 

 they would have full letters in the course of a fortnight from 

 Zanzibar, which would inform theon on what was known about 

 Dr. Livingstone and Mr. Stanley, and in the meantime he could 

 only say that the telegram was credible. 



We exceedingly regret to have to announce the death, after a 

 short illness (but too probably the effect of overwork), of Mr. 

 George Robert Gray, F. R. S., Senior Assistant Keeper of the 

 Zoological Collections in the British Museum, and an ornitholo- 

 gist of world-wide reputation through his numerous works. Of 

 these we need only particularise two — but two such as have 

 never been executed by any other man— the " Genera of Biuls,'' 

 in three fulio volumes (1S44-1849), illustrated by the late Mr. 

 Mitchell, some time secretary of the Zoological Society, and by 

 Mr. Wolf, showing an amount of labour at that time unparal- 

 leled ; .and the " Hand-list of Birds," only completed last year, 

 and compiled with a like amount of assiduity. Both these a e 

 works found to be indispensable by advanced students of O.-ni- 

 thoiogy in every country ; a fact which is alone sufficient proof 

 of their value. The magnificent bird gallery in the British 

 Museum, probably the most popular portion of that buildin"-, 

 owes its chief importance to Mr. Gray's labours ; and we hope 

 that, in selecting a successor to fill his post, the trustees will nr)t 

 hold thems'.-lves bound by any rule of routine, but will take care 

 that the officer in whose charge the splendid collection will be 



