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Profs. Percy Frankland and Marshall Ward. 



I select the following series of observations in illustration from a 

 large number which I made for my own guidance : it does not seem 

 necessary to publish all the notes, but as many readers may be 

 unacquainted with the magnitude of the dangers referred to, I retain 

 one or two experiments of a somewhat obviously elementary nature. 



In order to understand the behaviour of the thermometer as an 

 indication of what was going on in the culture-chambers, it was 

 clearly necessary that I should make a series of blind experiments in 

 which the bulbs of the thermometers were as carefully placed in the 

 relative proper positions as possible. 



The following series refer to the sort of temperature changes to be 

 expected in the laboratory, near a south window, in spring. 



Series 1 (an extreme Case). 



Changes of temperature as indicated by thermometers (A) lying 

 on table beside microscopes ; (B) hanging in glass bell-jar exposed 

 to light ; (C) hanging in darkened bell-jar. ; (D) on a stool in the 

 shade and much nearer the hot- water pipes which warmed the room. 



Obviously this kind of thing would not do for the experiments 

 contemplated, and the first thing I set myself to overcome was the 

 variations due to direct insolation, for it was found that the tempera- 

 ture of the air in the room used is remarkably constant, from the 

 regular action of the heating apparatus, and the rise in temperature 

 during the day and the fall during the night are comparatively small 

 and slow, provided the nights are not frosty and that the Venetian 

 blinds are drawn in the evening. 



Series 2 (Average Cases). 



Thermometer readings when the bulb is placed between blue and 

 red glasses, over the mirror of the microscope and in the position of 

 the hanging drop. 



