430 



B. Measurement of Temperature, Hu.miuity, 

 AND Air Movement. 



Most of the earlier temperature records were made with standard 

 thermographs placed adjacent to the bottles containing the codling moths 

 or placed in the cages containing insects inhabiting plants. In the latter 

 work a Leeds and Northrup resistance thermometer recorder, carrying 

 ten resistance thermometers, was used. These thermometers are approxi- 

 mately 1 by S cm. and can be inserted into small cavities or places in soil 

 or in the branches of a food plant. They are by far the most accurate 

 of all thermometers on the market, being correct to 0.2° (the unavoidable 

 error is due to shifting of the paper). This recorder, furthermore, has 

 the great advantage of eliminating the difficulty which results from hav- 

 ing the thermometer in one place and the animals in another with a degree 

 or two difference in temperature, as is usually the case. Where thermo- 

 graphs were used an effort was made to eliminate this difficulty by taking 

 regular readings of a mercury thermometer. 



Humidity was recorded by Friez hygrographs (human hair type) 

 which were checked weekly with a sling, or by daily readings of wet and 

 dry bulb thermometers enclosed in a tube. 



Evaporation was measured by the Livingston atmometer. The rate 

 of air f^ow was measured by use of the diaphragm chambers and Ellison 

 gage (Hamilton '17). The flows are readily measured by this method, 

 but it offers no adequate means of maintaining the flow as constant. In 

 practice, flows were set principally by the use of screw compression 

 clamps on rubber hose. In some cases, mercury valves were installed, 

 which consisted merely of a U-tube containing a small amount of mer- 

 cury. A slight rise in pressure would push the mercury around in the 

 U-tube and allow some air to bubble out. Generally, the flows were 

 simply set by the compression cock at intervals of a few days, and the 

 mean of the readings taken as indicating the rate of flow. 



Instrument records. The record sheets from the thermograph and 

 hygrothermograph, except where temperatures were practically constant, 

 and in many cases where they were not, were treated according to a 

 definite routine plan. The means for each two hours of the day were 

 first determined by inspection, a clerk being employed to write with a 

 lead pencil the mean number of degrees and the mean per cent of humidity 

 for the two hours in the proper space immediately below the graphs. 

 Each sheet was then checked by another clerk, corrected if any mistakes 

 were found, and returned for inking. The person doing the checking 

 often did the inking, so that the presence of the two-hour means in ink 

 indicated that the work had been checked over by a second person. The 

 sheets were then gone over a second time and means for half-days com- 

 puted. These half-days were taken as from eight to eight, and the mean 

 was composed of the sum of six two-hour means. These were then 

 written on the sheets in lead pencil with the eight o'clock hours indicated 

 by vertical lines. The period from eight to eight was taken because in 



