292 



SCIENTIFIC NEWS. 



[Mar. 



SCIENTIFIC TABLE TALK. 



■ By W. Mattieu Williams, F.R.A.S., F.C.S. 



Among the humiliating failures of modern science a pro- 

 minent place must be assigned to the attempts that have 

 been made to determine the temperature of the sun. 

 The problem appears at first glance simple enough. We 

 know the temperature of the solar rays that reach the 

 earth, and we also know that radiant heat, and all other 

 radiant energy, is diffused in suchwise that, like gravita- 

 tion, it must vary inversely with the square of the 

 distance from the radiating body, and thus, as Sir John 

 Herschel says, "the heat received on a given area 

 exposed at the distance of the earth, and on an equal 

 area at the visible surface of the sun, must be in propor- 

 tion to the area of the sky occupied by the sun's apparent 

 disc to the whole hemisphere, or as i to about 92,000." 

 (" Outlines of Astronomy," section 396.) 



The data thus expressed being so definite, we may 

 suppose that if eminent mathematicians have attempted 

 to solve the problem they will nearly agree in their 

 results. The reader who is not already acquainted with 

 these results will, therefore, be surprised by the following 

 figures, Newton's estimate is 1,699,300° Fah. Secchi 

 originally contended for a temperature of about 

 18,000,000°. Fah., and afterwards lowered his estimate 

 to 250,000°. Ericsson puts the figure at 4,000,000° 

 or 5,000,000". ZoUner, Spoerer, and Lane name tem- 

 peratures ranging from 50,000° to 100,000° Fah., while 

 Pouillet, Vicaire, and Deville have put it as low as 

 between 3,000° and 10,000° Fah. (Young, " The Sun"). 

 Rosetti states the effective temperature of the sun to be 

 18,000. Cailletet says 2,000° C, and VioUe 1,400'! to 

 2,500° C. Trowbridge and Hutchings estimate that the 

 temperature of the solar surfaces approximate to that 

 of the voltaic arc. This is based on recent researches, 

 in which the behaviour of carbon at various temperatures 

 in the laboratory is directly compared with that of carbon 

 in certain parts of the sun. 



It is, of course, very presumptuous and hazardous for 

 so feeble a mathematical machine as myself to discuss 

 this subject at all, but, in spite of this, I venture to 

 suggest that some of the excessively high temperatures 

 among the above have been obtained by the misuse of 

 those convenient mathematical fictions — the point without 

 dimensions, and the surface without thickness. 



In reasoning upon the gravitation of the sun, a planet, 

 or any other mass of matter, it is convenient to assume 

 that the whole mass is situated at one point — its centre of 

 gravity. This, of course, is a fiction, but it leads to no 

 error, provided the reasoner does not assume that any 

 portion of the mass possesses any such gravitating energy, 

 and no one does this. Neither does anyone, in consider- 

 ing the energy of gravitation at the surface of such body 

 (the earth, for example), imagine that such energy is 

 superficial. Everybody knows that the force which 

 brings a body from a height of 16 ft. down to the surface 

 of the earth in a trifle less than a second does not reside 

 merely on the surface of the earth, but is the resultant 

 of the gravitation of the whole of the earth's mass. 



Those who reason upon the temperature of the sun by 

 ascribing to his surface an intensity of temperature suffi- 

 cient to do the work he is known to do, perpetrate a 

 fallacy corresponding to that of assuming that the whole 

 of his enormous gravitating energy is concentrated upon 

 . his mere surface, 



Everybody knows that a big fire gives out more heat 



than a little one, and glass blowers, who avail them- 

 selves of radiant heat from a limited area (as in the 

 " glory-hole " furnace), know that the radiant energy 

 varies with the depth of the fire measured from front to 

 back, even though its face surface remains the same. 

 The temperature odhe big fire or deep fire burning in a 

 certain manner is no greater than that of a small fire or 

 hallow fire burning similarly. In chapters 7 and 8 of 

 " The Fuel of the Sun " I have stated in detail the 

 results of my researches on the transparency and 

 diathermancy of flame, which show that flames; 

 radiate through each other in suchwise that if one flame- 

 is placed behind another equal flame the amount of heat; 

 and light radiated from the front of the foremost and the- 

 back of the hindmost is twice as great as from either- 

 alone, and this -without any sensible increase of the- 

 temperature or luminosity of either. I carried the- 

 experiments up to 17 flames thus arranged, without 

 reaching any well-marked limit to their transparency 

 or diathermancy, i.e., the radiations of all the 16 flames- 

 behind passed through the one whose front was pre- 

 sented to the photometer and thermometer, each one- 

 adding its share to the sum total of radiant energy, or^ 

 otherwise stated, the radiant energy of a flame of giver* 

 temperature and brilliancy varied with its thickness, so 

 far as my experiments went. Whether this would still 

 be maintained if a thousand flames were radiating: 

 through each other, or a mass of flame of thickness 

 measurable in miles, I cannot affirm ; but the experiment 

 justified the conclusion that all the known effects of solar 

 radiation, both thermal and luminous, may be produced) 

 by a flaming envelope (the photosphere) having a tem- 

 perature corresponding to that of our ordinary gas- 

 flames burning under similar conditions of pressure^ 

 provided the depth or thickness of such flaming envelope 

 is sufficiently great. 



We all know that a paraffin lamp with a duplex wick 

 gives more light than with a single wick, although the- 

 outside broad radiating surfaces of the flame are equal in. 

 both cases. In the "Lucigen" and the "Doty "lamp, 

 this principle is carried still further. Here we have a> 

 huge flame 3 ft. or 4 ft. long and a foot or more in thick- 

 ness, but with an intrinsic or specific luminosity de- 

 cidedly below that of an ordinary paraffin lamp. These- 

 large flames are used for lighting large out-of-door spaces^ 

 as substitutes for daylight, where large numbers of work- 

 men are employed at night time. Iron, of March i6th, 

 tells us that a newspaper was read at 135 ft. from a 

 Doty Light, at Deptford. I find it difficult to do this at 

 13^ ft. from my study lamp. Applying the law of 

 inverse squares, as it has been applied by some in mea- 

 suring solar temperature and luminosity, we should 

 conclude that the flame of the Doty lamp is 100 times, 

 more brilliant and 100 times hotter (its thermic radiations- 

 correspond with the luminous) than an ordinary lamp, 

 which is absurd. Quantity of energy, as well as intensity 

 of action, has to be considered. We can no more deter- 

 mine the temperature or luminosity of the solar surface 

 by its distant radiant results, than we could predicate the 

 velocity of a moving body by only knowing its momen- 

 tum, or vis viva, without also knowing its mass. 



Superannuation of Professors. — It is proposed at 

 Paris to fix sixty-five as the age of superannuation for all 

 future professors, seventy being allowed for those holding 

 chairs at present. 



