METHODS OF CULTIVATION. 



183 



ture, and to have a small constant jet of gas at 

 the side of the burner, in a position to relight the 

 gas coming through the thermostat to the burner 

 when the valve is opened by the falling of the 

 mercury. The gas for this side jet does not pass 

 through the burner or the thermostat. 



When the experimenter is so situated that he 

 cannot obtain a supply of gas, the problem of 

 regulating temperature is not 

 quite so simple ; but the result 

 may be accomplished by the use 

 of a magneto-electric thermostat 

 invented by the writer some years 

 since. 



The regulating thermometer, 

 Fig. 8, may be made as in the 

 thermostat just described ; but, 

 instead of a tube conveying 

 gas, the mercury, when it rises 

 through the tube c to the space 

 above the cork d, meets at a cer- 

 tain point adjustable the in- 

 sulated platinum wires e and /, 

 completing an electric circuit. A 

 constant battery is required, 

 a single cup is sufficient, and 

 an electro-magnet, the lever of 

 which is made, by some simple 

 contrivance, to cut down the flame of the kero- 

 sene or alcohol lamp used as a source of heat. 



This electro-magnetic regulator may also be 



05 



Fig. 8. 



