SHOOTING STARS. Ill 



and bridegroom started for Switzerland, taking London and 

 Paris in their way. They returned to Oak Field, 23rd 

 September, to reside till 9th April, 1849, when they entered 

 their house in Acton Square, Salford. 



Joule continued his experiments for the mechanical 

 equivalent of heat in his laboratory at Oak Field. 



He was also pursuing the theoretical extension of the 

 dynamical theory of heat resulting from his discoveries. 



Early in 1848 he communicates to the PJiilosophical 

 Magazine the paper " On Shooting Stars," already referred 

 to. In this paper he makes a definite estimate of the resis- 

 tance encountered by a meteorite of the size of a six inch 

 cube, moving at the rate of eighteen miles a second, through 

 an atmosphere of one hundredth the density of that at the 

 earth's surface, and finds this to be 5io,6oolb. He then 

 determines the heat equivalent of this resistance, if the stone 

 traverses twenty miles, equal to raising 6,969,9801b. of water 

 i° Fahrenheit. He then continues : — 



" Of course, the larger portion of this heat will be given 

 to the displaced air, every particle of which will sustain the 

 shock, while only the surface of the stone will be in violent 

 collision with the atmosphere. Hence the stone may be 

 considered as placed in a blast of intensely heated air, the 

 rieat being communicated from the centre to the surface by 

 conduction. Only a small portion of heat will be received 

 by the stone, but if we estimate it at only one hundredth, 

 it will still be equal to i° Fahrenheit per 69,6791b. of 

 water, a quantity quite equal to the melting and dissipation 

 of any materials of which it may be composed. 



" It appears to me that the varied phenomena of meteoric 

 stones and shooting stars may all be explained in the above 

 manner, and that the different velocities of the aerolites, 



