74 Proceedings. 



The President (Dr. Schuster) remarked that the oil 

 and the water theories might be reconciled. Whether a 

 tree is struck by lightning or not may be determined by 

 the amount of oily matter it contains ; but once a tree is 

 struck the discharge will chiefly pass through the moisture, 

 and the damage will be greatest in those layers which con- 

 tain the greatest amount of moisture. He also alluded to 

 communications on the subject made to the Society in 

 1873 by the late Mr. Baxendell, and to experiments per- 

 formed at that time by Professor Reynolds to test the 

 explosive force of small quantities of moisture volatilised 

 by the electric spark, the results of which were communi- 

 cated to the Society in the same year. 



Dr. James Bottomley read an additional note to his 

 paper on " A method of Integration applicable to certain 

 partial Differential Equations." 



Dr. Schuster, F.R.S., read the following " Note on 

 Accurate Weighing " : — 



"Two methods are generally given to determine the 

 mass of a body when great accuracy is required. One is 

 Borda's method of substitution, the other is generally 

 ascribed to Gauss, and may be referred to here as that of 

 interchanging weights. The methods, really identical in 

 principle, are too well known to need further description. 

 The present note refers to the method of double weighing, 

 which is above criticism in itself, but the way in which it is 

 generally explained seems to me to be defective, and the 

 practice of the method as given in several standard treatises 

 on practical physics is faulty in so far as it involves one 

 weighing which is useless, and causes, therefore, loss of 

 time, which may be better employed in otherwise increasing 

 the accuracy of the determination. Let M be the mass of 

 the body required, the operator is instructed to find the 

 apparent weight when it is placed on one side of the 

 balance, say P, to repeat the weighing when the body is on 



