New York Agricultural Experiment Station. 133 



in all four chambers; for temperatures above 30° they are in parallel, 

 but for temperatures as low as 25° they are in series. This 

 arrangement allows four times as much current to pass through the 

 heaters for the higher temperatures as through those for the lower 

 ones. With stationary shelves this arrangement of the wires would 

 have presented no difficulties; but it was desired in this case to 

 have removable shelves. To accomplish this the ends of the heat- 

 ing wires are fastened to copper plates at the edges of the shelves; 

 and when the shelves are in position these plates are in contact 



FF 



TO I8°C CHAMBER 

 WIRED LIKE 25° CHAMBER**— 



• — « 



L-_ 4> 'TO30<>G CHAMBER . „ 



-^^ WIRED LIKE37° CHAMBER 



Fig. 5.— Arrangement of Circuits. 

 T, thermostat; R, resistance wires; C, copper plates; FF, Fuse.?. 



with the metal pegs that support the shelves. In each chamber 

 two of the supporting posts CC are faced with copper; and as this 

 copper is connected by wire with the thermostat and the main 

 circuit, the current passes through the heating wires whenever the 

 thermostat is closed. This arrangement of the heaters places them 

 well out of the way and distributes them so as to prevent over- 

 heating at any part of the chamber. To avoid the difficulty of 

 wiring beneath the shelves, the heaters might have been placed 

 vertically at each side of the chamber. This lateral arrangement, 

 although not tried out here, might prove fully as satisfactory. 



