102 PROCEEDINGS OF SECTION A. 



these burners (its switch being always on) can be turned up 

 directly on entering the room. The slate tables are supported by 

 piers going down to the shale and set in brick and cement, but in 

 cases where the floors are of wood the frame work is independent 

 of these piers. In many of the rooms a second slate slab is 

 provided at a convenient distance above the first in order to 

 accommodate galvanometers. The whole of the western half of 

 the building is free from iron as far as construction goes, and the 

 pipes are of copper. The bidcks tested from time to time during 

 the buikling work were found to be fairly non-magnetic, and in 

 fact experiments lately made have shown that the horizontal 

 intensity of the earth's magnetism is almost the same inside the 

 building as it is outside. In the rooms provided with steady 

 floors these are obtained by removing the earth and tilling in with 

 broken stone right down to the shale — in some cases to a distance 

 of ten feet. On the top of this carefully arranged stone heap is 

 a layer of concrete a foot thick. Above this is some fine white 

 sand and on this are laid hexagonal artificial (asphalt) gTanite 

 blocks ground flat on the top and carefully levelled. These blocks 

 are two inches thick ; and the floors as far as tested seem satis- 

 factory. One advantage of these blocks is that if it be desired to 

 fasten down any apparatus to the concrete the blocks can easily 

 be lifted, and if necessary replaced. The fine sand is designed 

 to prevent the transmission of vibration from one pai't of the floor 

 to another. 



ELECTRIC ARRANCxEMENTS. 



The details of the wiring need not be given as they present no 

 special features — except in the trouble that has been taken to 

 obtain high insulation. The wires are everywhere in places where 

 they can be got at ; and the fuses have been reduced to a minimum. 

 The arrangements for cutting out the different portions of the 

 system are very simple ; a switch-board wdth four switches is 

 placed in the corridor so as to break up the service into four 

 sections. The details of the Electric Supply have been already 

 given as far as the connections in the rooms are concerned. The 

 binding screws being below the projecting edges of the working 

 benches, have to be protected against possible wetting from fluids 

 spilt in the process of experimenting. This is attained by cutting 

 a groove on the under surface of the projecting part of the 

 benches. The whole of the lighting and supply circuits are led 

 on to a switch-board in the Battery House, This structure is a 

 glass louvred building standing thirty feet away from the east end 

 of the Laboratory ; it is about thirty feet long by twenty wide. 

 A horse-shoe dais is constructed on the concrete floor — and this 

 dais supports the fiftyfive E. P. S. Cells, designed to furnish the 

 current. In this house there is also a large trough-like sink, a 

 long wooden bench, and in general all conveniences for preparing 



