1910] Determining optimums of Temperatrue and Moisture 151 



The water within the jacket is heated in coil I (fig. 2) by means 

 of kerosene burner L (fig. 2). The method of heating could be 

 greatly improved where constant electric current is available b^^ 

 the installation of electric heaters under chamber E (fig. 3) and 

 the controlhng of the amount of current delivered by some form 

 of thermostat. This portion of the incubator was devised and 

 constructed by the "International Instrument Company," and 

 later so modified by the writer as to fit it for his use. 



Moisture Phase. 



While certain companies would undertake the construction 

 of constant low^ temperature incubators, we were unable to obtain 

 a combination constant low temperature and moisture incubator. 

 On the arrival of the constant low temperature incubator, we set 

 about devising a means of bringing the relative humidity under 

 control. After trying many things the writer adopted the method 

 of placing enough plants or water vessels in chamber E (fig. 3) to 

 bring the relative humidity to 100°, then when the relative humid- 

 ity reached the desired point to pre\-ent its further rise by passing 

 the air over calcium chloride. 



An exhaust fan A (figs. 2 and 3) was placed in the rear wall 

 of the chamber E and the air led through a 2 J" passageway into 

 a leaden box F (fig. 3) partly filled with calcium chloride, and 

 from there through a similar passageway B (figs. 2 and 3) back 

 into the chamber. The fan, passageways, and leaden box are all 

 included in the packing space of the incubator w^all. A strand of 

 human hair, after having the oil removed from it with sulphuric 

 ether, was stretched in an adjustable brass frame. A lever was 

 attached by its short arm to this hair in such a way that variation 

 in the length of the hair strand would cause the distal end of the 

 long arm to move through a considerable space. To this end of 

 this arm was attached a platinum electrode which descended into 

 a mercury-filled tube. Of course, the contact of the plati- 

 num point and the mercury was designed to close magnetic 

 circuit P (figs. 2 and 3) and this to close motor circuit Q (fig. 3) 

 which would set the exhaust fan in motion. So long as the plati- 

 num point remains in the mercury, the fan continues to change 

 the air. Less than a minute after the connection is made is 

 usually sufficient to dry the air to a point at which the contraction 

 of the hair breaks the connection. 



