Curiosities of Science. 63 



some hours. The Bunker-Hill monument, near Boston, U.S., 

 is higher in the evening than in the morning of a sunny day ; 

 the little sunbeams enter the pores of the stone like so many 

 wedges, lifting it up. 



In winter, the Earth is nearer the Sun by about $ than in 

 summer ; but the rays strike the northern hemisphere more 

 obliquely in winter than the other half year. 



M. Pouillet has estimated, with singular ingenuity, from a 

 series of observations made by himself, that the whole quantity 

 of heat which the Earth receives annually from the Sun is 

 such as would be sufficient to melt a stratum of ice covering 

 the entire globe forty-six feet deep. 



By the action of the sun's rays upon the earth, vegetables, 

 animals, and man, are in their turn supported ; the rays be- 

 come likewise, as it were, a store of heat, and " the sources of 

 those great deposits of dynamical efficiency which are laid up 

 for human use in our coal strata" (Herschel). 



A remarkable instance of the power of the sun's rays is re- 

 corded at Stonehouse Point, Devon, in the year 1828. To lay 

 the foundation of a sea-wall the workmen had to descend in a 

 diving-bell, which was fitted with convex glasses in the upper 

 part, by which, on several occasions in clear weather, the sun's 

 rays were so concentrated as to burn the labourers' clothes 

 when opposed to the focal point, and this when the bell was 

 twenty- five feet under the surface of the water ! 



CAUSE OF DAEK COLOUR OF THE SKIN. 



Darkness of complexion has been attributed to the sun's 

 power from the age of Solomon to this day, "Look not upon 

 me, because I am black, because the sun hath looked upon 

 me :" and there cannot be a doubt that, to a certain degree, 

 the opinion is well founded. The invisible rays in the solar 

 beams, which change vegetable colour, and have been em- 

 ployed with such remarkable effect in the daguerreotype, act 

 upon every substance on which they fall, producing myste- 

 rious and wonderful changes in their molecular state, man not 

 excepted. Mrs. Somerville. 



EXTREME SOLAR HEAT. 



The fluctuation in the sun's direct heating power amounts 

 to Ts tn > which is too considerable a fraction of the whole in- 



tensity not to aggravate in a serious degree the sufferings of 

 those who are exposed to it in thirsty deserts without shelter. 

 The amount of these sufferings, in the interior of Australia for 

 instance, are of the most frightful kind, and would seem far to 

 exceed what have ever been undergone by travellers in the 



