102 Mr. A. L. Fletcher on the 



obtained previously in a different way *, and was found to 

 agree well with the facts. Similarly we can equate the 

 expression for the latent heat and the temperature when the 

 former quantity is derived from the general law of molecular 

 attraction giving the arbitrary function a definite form. 

 But in every case the equation should reduce to the above 

 form. For example, Mills obtained in the above way from 



his law of molecular attraction that ^ = constant, 



which was found to agree well with the facts. Now we 

 have seen that according to the general law of molecular 

 attraction 



K 2 =|(2V%) ! , 



which reduces the equation to the same form as the 

 preceding. 



London, Oct. 27, 1910. 



XIV. The Radioactivity of the Leinster Granite. 

 By Aekold L. Fletcher. B.A.I.} 



THE granite of Leinster extends for a distance of 70 miles 

 along the East Coast of Ireland, having an average 

 width of 8 or 10 miles, and covering a land area of some 

 600 square miles. It extends in some places, near its 

 northern extremity, beneath the Irish Channel, and is by far 

 the largest granitic exposure in the United Kingdom. 



Its petrographical and mineralogical characters have 

 formed the subject of many memoirs which deal for the 

 greater number with special matters. The most important 

 treatise dealing generally with the petrology and mineralogy 

 of the granite is the paper by Professor Solias (Trans. R.I. A. 

 xxix. part xiv. 1891). 



The Leinster granite is throughout the main chain a true 

 granite, containing both biotite and muscovite micas. This 

 character applies also to most of the outlying exposures of the 

 rock. In two cases, Nos. 10 and 11 in the table on p. 106, 

 biotite granite or granitite is found in such exposures; while 

 in the cases of Nos. 1, 12, and 13 in the table, the mica is 

 mainly of the white variety. In all the granites dealt with, 

 with these exceptions, both micas are found. 



* Phil. Mag-. Oct. 1910, p. 688. 

 t Communicated by the Author. 



