440 



Mr. W. Galloway. [Mar. 23, 



best possible results by their explosion. Accordingly, in all the suc- 

 ceeding experiments the driving wheel was turned rapidly 200 times 

 instead of 100 times as before, the attendants relieving each other at 

 the work, and, thereafter, the results were much more uniform, and, 

 consequently, more satisfactory. 



It will be recollected from the account given in No. Ill paper, that 

 the gallery consists of seven sections, and that each section has a door 

 18 feet long by 2 feet 3 inches wide, which constitutes one of its sides 

 when it is closed (see sections a and b, fig. 3). When all the doors 

 are open the gallery has only three sides — namely, top, bottom, and 

 back, and its interior is exposed to view from one end to the other. 

 The doors then stand out horizontally on a level with the top to 

 which they are binged, while their free edges are supported on 

 suitable props. The table given below shows how many doors were 

 shut, and how many were open when each experiment was made, the 

 shut ones being, of course, those nearest the explosion chamber. In 

 one or two experiments, however, there were three doors next the 

 explosion chamber closed, the following three open, and the last one 

 shut. This was the case, for example, in the sixty-third experiment. 

 There is no provision in the table for showing this arrangement, and 

 as the flame did not, on any of these occasions, extend to the last 

 section, it was not considered worthy of a special column. Each of 

 the seven sections contained coal-dust in the cases referred to, and 

 that is the reason why they are all represented in the table. 



There were sets of three shelves, one above the other, placed trans- 

 versely in the gallery at the following points, measured from the 

 diaphragm towards the open end : 10 feet, 21 feet, 32 feet 6 inches, 

 42 feet, 56 feet, 65 feet, 76 feet 4 inches, 87 feet, 96 feet 8 inches, 

 107 feet, and 117 feet 6 inches. The spaces between the shelves of 

 each set, and between the highest and lowest shelf and the top and 

 bottom of the gallery, were intended to have an approximately equal 

 area. The shelves were about 6 inches wide by f inch thick. 



Those heaps of powder referred to in the table, whose distances from 

 the diaphragm correspond to the position of certain of the sets of 

 shelves, were in these instances placed on the top shelf, the others 

 were laid on the floor. 



After each experiment the coal-dust was entirely swept out and 

 replaced by fresh dust, except in one or two cases which are specially 

 mentioned in the table. 



The diaphragm usually consisted of six single sheets of newspaper, 

 but the exceptions are shown in the table. Where a note of interroga- 

 tion occurs the number of sheets may be taken as six, although the 

 real number was omitted in taking notes at the time. 



Fig. 1 shows the length of flame (measured from the diaphragm) 

 obtained in the principal explosion of each group. 



