I ^o 



Annals Entomological Society of America [Vol. Ill, 



reduce the error of the average to a ncgliKii)le quantity, or he 

 must deal with smaller numbers under conditions in which the 

 important varial)lcs are reduced to constants. 



In ])lanning a study of the life economy of certain insects most 

 injurious to staple crop production, the writer has adopted the 

 I)lan of using the smaller number of individuals and of reducnig 

 the numl)er of \arial)les to a minimum. Of course it has been 

 easy to eliminate natural enemies and to prevent large variation 

 in the ciuantitv and cjuality of food sup])ly. but of the physical 

 factors he has thus far been able to reduce only temperature and 

 moisture to constants. This has been accomplished through the 

 construction of an incul)at()r. in which, within limits, desired 

 degrees of each can l)e maintained. 



Construction of the Ai'1'.\r.\tus. Pl.vtes XXI-XXII. 



Ti:.\lI'HRATURE Ph.\SE. 



Essentiallv the incubator consists of a water-jacketed chamber 

 E (figs. 2 and-,) with sjK-cial pro\-ision for heating and cooling the 

 water within the jacket, the whole being surrounded by a box 

 filled with non-conducting packing.. The packing used in this 

 instance consisted of wood shax'ings. The i 2" x 1 2" x 18" cham- 

 ber is jacketed on three sides only, the fourth being closed by a 

 double glass door for the purpose of admitting light. The water 

 is cooled l)y the inflow of ice water from tank G (Fig. 3). This 

 exchange is automatically controlled by means of mercurial 

 thermostat D (fig. 2), which i)rojects far into the jacket. 



Tlie i)latinum-tip])ed electrode U (tig. 2) has been so adjusted 

 that when the temperature of the water within the jacket rises 

 higher than is necessary to bring the air in chamber E (fig. 3) 

 to'the desired point, the rising mercury column in D (fig. 2) makes 

 contact with it and completes magnetic circuit N (figs. 2 and 3), 

 magnetizing electromagnet S (fig. ^). pulling lever T (fig. 3) down 

 upon it, thus pulling valve M out of its seat and allowing ice water 

 to flow by gravitv into the jacket. The pulling of the le\-er down 

 on the electromagnet S (fig. 3) completes motor circuit O (figs. 

 1 and 3) , and sets spiral lift C (fig. 3) in motion. This mterchange 

 imi)elled bv gravitv is thus hastened by pumping. '1 his inter- 

 change continues until enough cold water has been introduced 

 into the jacket to cause the mercury column in D (fig. 2) to with- 

 draw from the electrode U (fig. 2) . So soon as this happens valve 

 M (fig. 3) falls back into its seat and spiral lift C (fig. 3) stops. 



