. Research methods in ecology. Plant ecology. the liquid expands. This is due to the fact that the fluid expands too slowly to carry the marker upward, while the surface tension causes it to be drawn downward as the fluid contracts. The minimum temperature is indicated by the upper end of the marker. In setting up the thermome- ters, they are attached by special thumbscrews to a support which holds them in an oblique position. The minimum is placed in a special holder above the maxi- mum which rests on a pin that is used also for screwing the piv- ot-screw into po- sition. The sup- Fig. 17. Ma
. Research methods in ecology. Plant ecology. the liquid expands. This is due to the fact that the fluid expands too slowly to carry the marker upward, while the surface tension causes it to be drawn downward as the fluid contracts. The minimum temperature is indicated by the upper end of the marker. In setting up the thermome- ters, they are attached by special thumbscrews to a support which holds them in an oblique position. The minimum is placed in a special holder above the maxi- mum which rests on a pin that is used also for screwing the piv- ot-screw into po- sition. The sup- Fig. 17. Maximum-minimum thermometer. nort is screwed tightly to the cross-piece of a post, or in forest formations it is fastened di- rectly to a board nailed upon a tree trunk. A shelter has not been used in ecological work, although it is the rule in meteorological observations. The minimum thermometer is set for registering by raising the free end, so that the marker runs to the end of the column. The mercury of the maxi- mum is driven back into the bulb by whirling it rapidly on the pivot-screw after the pin has been taken out. This must be done with care in order that the bulb may not be â broken. As soon as the in- strument comes to rest, it is raised and the pin re- placed, great care being taken to lift it no higher than is necessary. When the night maximum is sought, the thermometer should be whirled several times in order to drive the column sufficiently low. Usually, in such cases, a record is made of this point to make sure that the maximum read is the actual one. If the pivot-screw is kept well oiled, less force will be required to drive the mercury back. In practice, the thermometers have been observed at 6:00 and 6:00 each day, thus permitting the reading of the maximum-minimum for both day and night. Pairs of maximum-minimum thermometers are to be obtained from H. J. Green, 1191 Bedford Ave., Brooklyn, or Juhen P. Friez, Baltimore, Maryland, at a cost of $
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