Mar., 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



61 



as " baroque ' has led to this, but it must be re- 

 membered that otoliths have the porcellanous texture 

 of the interior of the common oyster-shell and lack 

 the sheen and play of colours characteristic of mother- 

 o'-pearl. 



• • 



Fig. 8.— The Large Ear Stones of some other Flat Fish. 



Turning now to other orders of fishes we find that 

 while g-anoids such as the sturg-eon have more or less 

 well developed ear stones, the cartilaginous fishes, 

 such as sharks and skates, have in the sacculus a num- 

 ber of separated grains instead of a solid mass. 



Radivim— the Cause of 

 the Ea^rth's HeoLt. 



Professor E. Rutherford, F.R.S., has written an 

 interesting and most noteworthy article in the Februar) 

 number of Harper's Magazine under the above title. After 

 referring to the controversy between Geologists and 

 Physicists regarding the age of the earth, he discusses the 

 cause of the heat in the earth and the sun, and points out 

 that while the heat supplied by possible chemical com- 

 bination is inadequate to account for this, the fact that 

 radio-active bodies are able to emit a great amount of 

 heat throws quite a new light on the question. " In the 

 course of a year," says this great authority, " one pound 

 of radium would emit as much heat as that obtained from 

 the combustion of one hundred pounds of the best coal, 

 but at the end of that time the radium would apparently 

 be unchanged and would itself give out heat at the old 

 rate." And it is probable, he adds, that it would continue 

 to do so for about a thousand years. 



The author then describes how all radio-active bodies 

 must emit heat, although in lesser comparative amounts; 

 thus the heating effect of uranium is probably only 

 about one millionth part of that shown by an equal weight 

 of radium. Yet radio-active matter has been found to be 

 distributed, in minute quantities, throughout the atmo- 

 sphere and the crust of the earth. " These emanat ions are 

 not produced in the air itself, but are exhaled from the 

 earth's crust which is impregnated with radio-active 

 matter." Professor Rutherford then comes to a remark- 

 able conclusion. " Since the radio-active substances 

 present on the earth are continuously expelling a particles. 



heat must be evolved in amount proportional to the 

 quantity of active matter present and to the intensity of 

 the radiations. The question then arises, is the amount 

 of radio-active matter present in the earth sufficient to 

 heat it to an appreciable extent ? I think that even with 

 our present knowledge this question must be answered 

 in the affirmative." In support of this he continues, 

 " Since one gramme ofradium emits enough heat each hour 

 to raise one hundred grammes of water through 1° C., 

 a simple calculation shows that the present loss of 

 heat from the earth is equivalent to that supplied by 

 the presence of about 270 million tons of radium. This 

 amount may seem very large compared with the small 

 quantities of radium hitherto separated, but is small, for 

 example, compared with the annual output of coal from 

 the world. It can readily be deduced that this amount 

 of radium, if distributed uniformly throughout the earth's 

 crust, corresponds to only five parts in one hundred 

 million million per unit mass. This is a very small 

 quantity, and calculations based on the observations of 

 Elster and Geitel show that the radioactivity observed 

 in soils corresponds to the presence of about this propor- 

 tion of radium." 



CORRESPONDENCE. 



Spark Electrographs. 



To THE Editors of " Knowledge." 

 Sirs, — Re spark electrograph shown in your last issue. 

 During a series of investigations, made nearly two years ago, 



