174 Scientific Intelligence. 



ture of the moon to be a few degrees above the freezing point. 

 On the supposition that three-fifths of the heat is conducted 

 inward, Poynting calculates the upper limit at 29*7° A. He also 

 calculates the temperature of fully absorbing spherical bodies of 

 l cm in diameter at the distance of the earth from the sun and 

 finds the temperature = 300° A. This will be the temperature 

 of bodies smaller than l cm , so long as they are not too small to 

 absorb all the radiation falling upon them. The variation, of 

 temperature with distance from the sun is next estimated ; the 

 author regards it as highly probable that the temperature of mass 

 is everywhere below the temperature of freezing point of water. 

 The only escape from this conclusion is to suppose an appre- 

 ciable amount of heat issuing from his surface. Considering a 

 comet as made up of small particles of the order l cm or less, 

 these particles twenty-three million miles from the sun would 

 have the temperature of melting lead, and at three and three- 

 quarters million miles, the temperature of cast iron (1500°). 



Poynting then discusses the value of the radiation pressure. 

 Bartoli showed that a pressure must exist without any theory in 

 regard to the nature of light, beyond a supposition that a surface 

 ean move through the ether, doing work on the radiation alone, 

 and not on the ether in which the radiation exists. The most 

 interesting part of the paper is that which deals with a compari- 

 son between mutual gravitation and radiation pressure of small 

 bodies. Poynting calls attention to the fact, that if the radia- 

 ting body is diminished in size the radiation piessure due to it 

 also decreases less rapidly than the gravitative pull which it 

 exerts. The radiation decreases as the square of the radius of 

 the emitting body and its gravitational pull as the cube. It is also 

 noted that equality of action and reaction does not hold between 

 the radiating and receiving bodies alone. The ether is material 

 and takes its part in the momentum relations of the system. 

 Two globes of water, probably nearly full absorbers at 300° A, 

 will at that temperature neither attract nor repel each other if 

 their radii are about 20 cm . Small particles of the order l cm 

 radius would be drawn into the sun even from the distance of 

 the earth in times not large compared with geological times. 

 Near the sun the effects are vastly greater. The application to 

 meteoric dust in the system is obvious. The entire paper pleads 

 for an extension of our idea of matter to include the medium. 

 Bodies do not act upon each other ; each sends out a stream of 

 momentum into the medium surrounding it. Some of this 

 momentum is ultimately intercepted by the other, and in its pas- 

 sage the momentum belongs neither to one body nor to the other. 

 The action on one of the bodies is equal and opposite to the reac- 

 tion on the light-bearing medium contiguous to it. — Phil. Trans, 

 of Roy. tioc, Series A, vol. ccii, pp. 525-552. j. t. 



8. Ittondlotfs n-rays. — Blondlot describes a new species of 

 rays which he terms n-rays. These rays are given out by the Auer- 

 burner or still better by the Nernst lamp. They penetrate alumi- 



