GREENHOUSE AND LABORATORY 37 



a Meteorostat. My own is shown in position by the photo- 

 graph II. It is wholly of glass and metal, 2\ feet square, 4^ 

 feet high to the peak of the sloping roof, and rests on an iron 

 support 2 J feet high. It is not air-tight, but would be better 

 if it were. Originally it was warmed by water in a copper box, 

 4 inches deep, forming its bottom, the water being heated from 

 beneath by a gas-flame controlled by a thermo-regulator in the 

 case. To prevent the escape of gas-fumes into the house, the 

 flame was enclosed by an air-tight hood with inlet and outlet 

 tubes, 6 inches wide by 1 inch thick, leading out-of-doors. More 

 recently I have heated it by electricity from an incandescent 

 circuit, the current passing through a heating coil in a smaller 

 copper box of water in the bottom of the case, though this, owing 

 to defects in the regulator,* has been only partially satisfactory. 

 Cooling is effected by a coil of tin pipe in the top of the case, 

 through which cold water from the street pipes can be circulated; 

 this suffices to prevent undue heating when the temperature of 

 the house rises too high on bright days, though it is insufficient 

 to keep the case permanently much below the average tempera- 

 ture of the house. To promote a more rapid and even warm- 

 ing or cooling, small electric fans driven by a battery below the 

 case are installed beside the warming 'box and the cooling coil, 

 and their occasional use equalizes the temperature throughout 

 the case. Humidity is readily raised by placing a wet sponge 

 in front of one of the fans, and lessened by exposing shallow 

 pans of calcium chloride, though a tube through which air could 

 be driven over the calcium chloride by one of the fans would 

 be better. Light is tempered by a white curtain, and cut off 

 altogether by a hood, completely enclosing the case, made from 

 double black sateen. A recording thermograph and a hygro- 

 graph complete the arrangement. 



This meteorostat, though better than any other arrangement 

 I have seen, and ample for all student work, is yet only mod- 

 erately efficient; and I have designed a much better one, adapted 



* Simple, but apparently efficient, electric thermo-regulators are described by 

 Mast in Science, 26, 1907, 554. and by Cannon in the Plant World, 10, 1907, 262. 



