414 SCIENTIFIC RECORD FOR 1882 



dated vapors, this interchange being effected by the centrifugal action 

 of the sun itself. {Nature, xxv, p. 441.) 



As this theory has given rise to considerable discussion during the 

 past year, we give the following references : See (1) criticisms, E. D. 

 Archibald {Xature, xxv, p. 524), and Siemens's reply to him on the same 

 page; (2) criticisms of Charles Norris and T. Sterry Hunt, and Sie- 

 mens's reply. {Nature, xxv, pp. 601-603.) 



Fitzgerald raises several pertinent objections to Dr. Siemens's solar 

 hypothesis, to which a full reply is given by the author. {Nature, xxvi, 

 p. 80.) 



Crova communicates to the Paris Academy of Sciences the results of 

 ii year's experiment by a Government commission at Montpellier with a 

 solar mirror and boiler. (Similar experiments have been made at Con- 

 stantine.) The maxima of yield generally correspond to the minima of 

 intensity of radiations. The absolute quantity of heat utilized depends 

 essentially on the temperature of the air. In the climate of England it 

 is not possible to reach half the utilization attainable in the most favor- 

 able circumstances, and the sun does not shine continuously enough to 

 favor the practical use of the apparatus. {Nature, xxv, p. 596.) 



Next in order after the attempts to utilize the direct heat of the sun 

 must be mentioned the idea suggested by Mr. Milne, of Tokio, as to the 

 possibility of utilizing the internal heat of the earth. He states that 

 " there is an unlimited supply of energy in the interior of the earth, and 

 which crops out upon the surface in the form of hot springs, volcanoes, 

 &c. The heat of these springs could easily be converted into an elec- 

 tric current." {Nature, xxvi, p. 211.) 



We see no reason to doubt that ere long it will be found that the 

 cheapest method of warming some cities will be by means of hot water 

 and steam pipes, communicating with a deep artesian well. 



Professor Everett has presented an elaborate report on behalf of the 

 underground temperature committee of the British Association, contain- 

 ing a summary of all their results and preceding fifteen reports. This 

 is published apparently in full in Nature, xxvi, pp. 564-589. 



Passing by the innumerable details, we summarize the following gen- 

 eral conclusion: The mean increase of temi)erature per foot, as deduced 

 from all reliable observations throughout the whole world, is found to 

 be 0.01563, or about J^ of a degree Fahrenheit. This is a slower rate than 

 has been generally assumed. From this he deduces 0.000285 as the rate 

 in degrees centigrade per centimeter of depth. If this be multiplied 

 by the conductivity of the earth's crust, for which 0.0058 is adopted, 

 based on Herschel's and Thomson's results, we obtain H. 330+10-^" as 

 flow of heat across a square centimeter. If now this be multiplied by 

 the number of seconds in the year, we obtain 41.4 as our estimate of the 

 average number of gram-degrees of heat tnat escape annually through 

 each square centimeter of the earth's sub^ance. {Nature, xxvi, p. 591.) 

 Pouchet communicates to the Paris Academy of Sciences some obser- 



