158 Intelligence and Miscellaneous Articles. 



as water is practically incompressible, the sea remains essentially 

 unaffected, whilst the earth shrinks beneath it, and thus causes the 

 tide. The shrinkage of course becomes greater, and the tide higher, 

 when both sun and moon take part in the counter-pull, whether 

 acting on the same side of the earth or on opposite sides. It may 

 be assumed, however, from the known height of the tidal wave 

 where the march of this wave is unopposed, that the maximum 

 amount of contraction does not exceed a foot for each thousand 

 miles of the earth's radius — being thus, in round numbers, less than 

 one part in five millions. In the tremendous pull of the earth upon 

 the moon, by which the moon is kept upon its course, a passing 

 contraction of this comparatively slight amount may be easily con- 

 ceived to follow. According to the commonly adopted theory, one 

 tide is assumed to result from the withdrawal of the earth, locally, 

 from the waters above it ; in the view now proposed, both tides are 

 assumed (although on a different principle) to be thus caused. 



OX THE TEMPERATURE OF THE SUN. BY J, VIOLLE. 



Several months since, I undertook some experiments to deter- 

 mine, by various methods, the temperature of the sun. I beg the 

 Academy to kindly permit me to submit to it the first resulls of my 

 researches. 



Measurements of solar heat can be made in two ways. In the 

 first, a thermometer is placed successively during equal times in the 

 shade and then in the sun, and the course of the instrument is fol- 

 lowed in each case : this is the dynamic method, that of the pyrohe- 

 liometer of Pouillet. In the second the thermometer remains sub- 

 mitted to solar radiation until the temperature indicated by the 

 instrument becomes stationary ; and at the same time the tempe- 

 rature of the thermometer and that of the enclosure are noted : this 

 is the static method, that which appears to be adhered to by most 

 of the physicists who occupy themselves with the measurement of 

 solar heat. I shall for the moment speak only of the latter me- 

 thod, and in the first place consider its principle. 



Let a spherical envelope be maintained at a constant temperature 

 t, and let the bulb of a thermometer be in the centre of the sphere, 

 which bulb I will for an instant suppose infinitely small. The en- 

 closure is coated with lampblack, as well as the bulb of the thermo- 

 meter. Let us suppose equilibrium of temperature established. 

 The enclosure then sends to the thermometer a quantity of heat $«*, 

 a being Dulong's constant or 1*0077 ; and the thermometer sends 

 back to the enclosure the same quantity of heat S«*. Let us now 

 pierce hi the spherical enclosure a circular aperture w of such di- 

 mensions that it will be seen from the centre under the angle which 

 measures the apparent diameter of the sun, and let us direct this 

 aperture toward the sun. It is manifest, according to the law of 

 the variation of calorific intensity inversely as the square of the 

 distance, that the real action of the sun on the bulb of the thermo- 



