228 



Messrs. W. Macnab and E. llistori. 



experiments have been made on the lines above indicated, but a large 

 number of the results have had to be discarded. 



To begin with, one point which had to be studied was whether the 

 size of the grain of the explosive would make any difference in the 

 results ; but after numerous experiments we have come to the conclu- 

 sion that, within reasonable limits, the size of the grain exercises no 

 influence under the conditions of these experiments. 



In all the experiments about to be described, the explosives used 

 were all gelatinised preparations of gun-cotton alone, or mixed with 

 nitro-glycerine, all in the form of small grains, and the charges were 

 fired in the bomb full of air. 



; I A difficulty observed was that the deflections of the galvanometer 

 were different, everything else being equal, when the position of the 

 couples varied in relation to the position of the explosive. It l)ecame 

 necessary, therefore, to carry out a series of experiments in order to 

 determine which position of the couple gave greatest and most uniform 

 results. 



The following Table II gives the results of the experiments made 

 to find the hottest place in the bomb. The same charge of the same 

 explosive and the same couple were used in all the experiments, the 

 only difference being that the position of the couple in relation to the 

 explosive which was held in a platinum capsule. Three experiments 

 were made in each position. 



j Table II. 



'! Couple No. 5. 



Position of couple bent into capsule in centre 



of charge 



Couple 1" above explosion 



„ 2' „ 



„ 3t" „ (furthest practicable) 



These results are shown graphically in Diagram 1 , where the vertical 

 distance represents the deflection of the galvanometer, and the hori- 

 zontal the position of the junction of the couple in relation to the 

 charge. The deflection is least when the junction is embedded in the 

 charge, and greatest when about 3 inches above it. 



As will be seen from the diagram, there is very little variation in the 

 results between 2 J inches and 3^ inches (the maximum distance allowed 

 by the size of the bomb), and as the actual maximum was shown at 

 3 inches, we have in all future experiments placed the thermo-couple at 

 3 inches above the surface, of the charge. 



Deflection of light 

 in mm. 



Mean. 



118, 131, 130 126-3 



159, 156, 141> 154-6 



156, 163, 153 157-5 



168, 165, 163 165-5 



160-5, 168-5, 155-4 101 -4 



