Dr. J. R. Mayer on Celestial Dynamics. 417 



inches from the plate, or until the sparks resembled the dis- 

 charges of a small Ley den jar. The sparks never passed between 

 the point and circumference of the plate. It was otherwise when 

 T used a 7-inch plate. Hence the size of the plate connected 

 with the positive end of the coil must depend on the power of 

 the coil employed. The pointed wire used in all the experi- 

 ments was nearly \ of an inch thick. 



I have not as yet had time to give a fair trial to the coil with 

 a battery of greater power than that of three 4-inch cells. With 

 one cell in which the zinc plate was 4 inches by 8, I got sparks 

 8^ inches long when the plate connected with the negative end 

 was only 4 inches in diameter. Had I known at the time that 

 with a 12-inch plate the spark is 1J inch longer than with a 

 4-inch one, the sparks with the single cell 4x8 would have 

 been 9| inches long. I intend to try the coil as soon as conve- 

 nient with a battery of twelve 6-inch cells, and six cells 4 inches 

 by 8. 



St. Patrick's College, Mavnooth, 

 May 13, 1863. 



LVII. On Celestial Dynamics. By Dr. J. R. Mayer.] 



[Concluded from p. 409.] 



IX. The Heat of the Interior of the Earth. 



WITHOUT doubt there was once a time when our globe 

 had not assumed its present magnitude. According to 

 this, by aid of this simple assumption, the origin of our planet 

 may be reduced to the union of once separated masses. 



To the mechanical combinations of masses of the second order, 

 with masses of the second and third order, &c, the same laws 

 as those enunciated for the sun apply. The collision of such 

 masses must always generate an amount of heat proportional 

 to the squares of their velocities, or to their mechanical effect. 



Although we are not in a position to affirm anything certain 

 respecting the primordial conditions under which the con- 

 stituent parts of the earth existed, it is nevertheless of the 

 greatest interest to estimate the quantities of heat generated by 

 the collision and combination of these parts by a standard 

 based on the simplest assumptions. 



Accordingly we shall consider for the present the earth to 

 have been formed by the union of two parts, which obtained 

 their relative motions by their mutual attraction only. Let the 

 whole mass of the present earth, expressed in kilogrammes, 

 be T, and the masses of the two portions T — x and x. The 

 ratio of these two quantities may be imagined to assume various 



