April i, 1880] 



NATURE 



521 



last hundred years, and secured him, the modest apothe- 

 cary of Koping, a place in the first rank of the men of 

 science of all ages and of all countries." 



In a succeeding paper I propose to give a sketch of the 

 ■work of Scheele, and to return at the same time to the 

 chemical labours of Bergman. 



(To be continued) 



THE TEMPERATURE OF SPACE AND ITS 

 BEARING ON TERRESTRIAL PHYSICS 



FEW questions bearing directly on terrestrial physics 

 have been so much overlooked as that of the tem- 

 perature of stellar space, that is to say, the temperature 

 which a thermometer would indicate if placed at the outer 

 limits of our atmosphere and exposed to no other influ- 

 ence than that of radiation from the stars. Were we 

 asked what was probably the mid-winter temperature of 

 our island 11,700 years ago, when the winter solstice was 

 in aphelion? we could not tell unless we knew the tem- 

 perature of space. Again, without a knowledge of the 

 temperature of space, it could not be ascertained how 

 much the temperature of the North Atlantic and the air 

 over it were affected by the Gulf Stream. We can deter- 

 mine the quantity of heat conveyed into the Atlantic by 

 the stream, and compare it with the amount received by 

 that area directly from the sun, but this alone does not 

 enable us to say how much the temperature is raised by the 

 heat conveyed. We know that the basin of the North 

 Atlantic receives from the Gulf Stream a quantity of heat 

 equal to about one-fourth that received from the sun, but 

 unless we know the temperature of space we cannot say 

 how much this one-fourth raises the temperature of. the 

 Atlantic. Suppose 56 to be the temperature of that 

 ocean: this is 517" of absolute temperature which is 

 derived from three sources, viz. : (1) direct heat from the 

 sun, (2) heat from the Gulf Stream, and (3) heat from 

 the stars. Now unless we know what proportion the heat 

 of the stars bears to that of the sun we have no means of 

 knowing how much of the 517° is due to the stars and 

 how much to the sun or to the Gulf Stream. 



M. Pouillet and Sir John Herschel are the only 

 physicists who appear to have devoted attention to the 

 problem. The former came to the conclusion that space 

 has a temperature of — 142 C. or — 224 F., and the 

 latter, following a different method of inquiry, arrived at 

 nearly the same result, viz., that its temperature is about 

 - 239° F. 



Can space, however, really have so high a temperature 

 as — 239 ? Absolute zero is - 461'. Space in this case 

 would have an absolute temperature of 222' , and conse- 

 quently our globe would be nearly as much indebted to 

 the stars as to the sun for its heat. If so space must be 

 enormously more transparent to heat rays than to light 

 rays. If the heat of the stars be as feeble as their light, 

 space cannot be much above absolute zero, and this is 

 the opinion expressed to me a few weeks ago by one of 

 the most eminent physicists of the day. Prof. Langley is 

 also of this opinion, for he concludes that the amount of 

 heat received from the sun is to that derived from space 

 as much as four to one ; and consequently if our luminary 

 were extinguished the temperature of our earth would fall 

 to about - 360 F. 



It must be borne in mind that Pouillet's Memoir was 

 written more than forty years ago, when the data avail- 

 able for the elucidating the subject were far more im- 

 perfect than now, especially as regards the influence of 

 the atmosphere on radiant heat. For example, Pouillet 

 comes to the conclusion that, owing to the fact of our 

 atmosphere being less diathermanous to radiation from 

 the earth than to radiation from the sun and the stars, 

 were the sun extinguished the radiation of the stars 

 would still maintain the surface of our globe at - 89' C., 

 or about 53 C. above that of space. The experi- 



ments of Tyndall, however, show that the absorbing 

 power of the atmosphere for heat-rays is due almost ex- 

 clusively to the small quantity of aqueous vapour which 

 it contains. It is evident, therefore, that but for the sun 

 there would probably be no aqueous vapour, and conse- 

 quently nothing to protect the earth from losing its heat 

 by radiation. Deprived of solar heat, the surface of the 

 ground would sink to about as low a temperature as 

 that of stellar space, whatever that temperature may 

 actually be. 



But before we are able to answer the foregoing ques- 

 tions, and tell, for example, how much a given increase 

 or decrease in the quantity of sun's heat will raise or 

 lower the temperature, there is another physical point to 

 be determined, on which a considerable amount of un- 

 certainty still exists. We must know in what way the 

 temperature varies with the amount of heat received. 

 In computing, say, the rise of temperature resulting from a 

 great increase in the quantity of heat received, should we 

 assume with Newton that it is proportional to the increase 

 in the quantity of heat received, or should we adopt 

 Dulong's and Petit's formula? 



In estimating the extent to which the temperature of 

 the air would be affected by a change in the sun' s dis- 

 tance, I have hitherto adopted the former mode. This 

 probably makes the change of temperature too great, 

 while Dulong's and Petit's formula adopted by Mr. Hill 

 (Nature, vol. xx. p. 626), on the other hand, makes it 

 too small. Dulong's and Petit's formula is an empirical 

 one, which has been found to agree pretty closely with 

 observation within ordinary limits, but we have no reason 

 to assume that it will hold equally correct when applied to 

 that of space, any more than we have to infer that it will 

 do so in reference to temperature as high as that of the 

 sun. When applied to determine the temperature of the 

 sun from his rate of radiation, it completely breaks down, 

 for it is found to give only a temperature of 2130 F. 

 (Anier. Jour. Science, July, 1870), or not much above 

 that of an ordinary furnace. 



But besides all this it is doubtful if it will hold true in 

 the case of gases. From the experiments of Prof. Balfour 

 Stewart (Trans. Edin. Roy. Soc, xxii.) on the radiation 

 of glass plates of various thicknesses, it would seem to 

 follow that the radiation of a material particle is probably 

 proportionate to its absolute temperature, or, in other 

 words, that it obeys Newton's law. Prof. Balfour Stewart 

 found that the radiation of a thick plate of glass increases 

 more rapidly than that of a thin plate as the temperature 

 rises, and that, if we go on continually diminishing the 

 thickness of the plate whose radiation at different tem- 

 peratures we are ascertaining, we find that, as it grows 

 thinner and thinner, the rate at which it radiates its heat 

 as its temperature rises becomes less and less. In other 

 words, as the plate grows thinner its rate of radiation 

 becomes more and more proportionate to its absolute 

 temperature. And we can hardly resist the conviction 

 that if it were possible to go on diminishing the thick- 

 ness of the plate till we reached a film so thin as to 

 embrace but only one particle in its thickness, its rate 

 of radiation would be proportionate to its temperature, 

 or, in other words, it would obey Newton's law. Prof. 

 Balfour Stewart's explanation is this : As all substances 

 are more diathermanous for heat of high than low 

 temperatures, when a body is at a low temperature only 

 the exterior particles supply the radiation, the heat 

 from the interior particles being all stopped by the 

 exterior ones, while at a high temperature part of the heat 

 from the interior is allowed to pass, thereby swelling the 

 total radiation. But as the plate becomes thinner and 

 thinner, the obstructions to interior radiation become less 

 and less, and as these obstructions are greater for radiation 

 at low than high temperatures, it necessarily follows that, by 

 reducing the thickness of the plate, we assist radiation at 

 low more than at high temperatures. 



