170 ANNUAL OF SCIENTIFIC DISCOVERT. 



ugal force, was supposed to push them more widely asunder. 

 So he twirls the wciglit at the end of the spring, in the open air. 

 It tends to fly away ; the spring stretches to a certain (sxtent, and 

 as the speed of re\olution is augmented, the spring stretches still 

 more, the distance between tlie hand and the weiglit being thus 

 increased. The spring rudely figures tlie force of cohesion, while 

 the ball rejn'csents an atom under tlie inlliience of heat. 



The intellect, he truly says, knows no ditrerence between great 

 and small. It is just as easy, as an intellectual act, to picture a 

 vibrating or revolving atom as to picture a vibrating or revolving 

 cannon ball. These motions, however, are executed within limits 

 too minute, and the moving jjarticles are too small, to ]n\ visible. 

 Here the imagination must help us. In the case of solid bodies, 

 you must conceive a power of vibration, within ceitain limits, to 

 be possessed by the molecules. You must supjiose them oscilla- 

 ting to and fro; the gi-eater amount of heat we imi)art to the 

 body, the more rapid will be the molecular vibration, and the 

 wider the amplitude of atomic oscillation. — All the Year llnimd. 



CORRELATION OF THE PHYSICAL FORCES. 



There are signs of some reaction against that doctrine of the cor- 

 relation of the physical forces which, for the last twenty 3'ears, has 

 so dominated scientific tiiought, or, at least, against that interpre- 

 tation of it which makes it teach that all forces are modifications 

 of one force, and are mutually convertil)le into each other. Thus, 

 in the last numl)er of the " Quarterly .Journal of Science," a men- 

 tion, in an article on "I)e La Hue and Celestial Fhotogra])hy,'" of the 

 appearance in the photographs of the solar eclipse of i860 of solar 

 prominences invisible to the human eye, calls forth the following 

 very noteworthy remarks: " A curious question arises from the 

 consideration of the chemical p(jwer evidently possessed by th(;se 

 liroiiiinences, be they llames or clouds. We never, as we have 

 already stated, imder ordinary circumst;mces, obtain an impressed 

 image of the sun without linding the indications of a protected 

 circle — that is, one which ])roves a paucity of chemical power — 

 surrounding the photographic disk. Yet, when the light of the 

 solar disk is interrupted b^' the body of the moon, the radiations 

 proceeding from the edge, or rather, perhaps, from beyond it, have 

 a strong photographic i)ower. What is the cause of this most 

 remarkable difference? Why is it that the photograpliic tablet is 

 impressed during an eclipse by objects which do not give light 

 enough to be visible even at the period of totality, and that they 

 do not effect the required chemical change upon our sensitive 

 plates when the sun is unobscured ? The only reply which we are 

 at present in a position to give, is, that the diffused light when the 

 sun is shining is sufficiently jjowerful to overcome the weaker 

 chemical radiations of those solar clouds or flames. If this rejjly 

 approaches correctness, we have additional evidence confirming 

 the view that the two principles existing in the sunbeam, light or 

 luminous pow^er, and actinism or chemical power, are not uK^difi- 

 cations of the same ' energy,' to use the accepted term of the day, 



