on Vegetables, with reference to their Temperature. 3 



serious attention : the state of the atmosphere has been omitted, 

 and in other respects the data are so imperfect, as to exclude 

 the possibility of our repeating any of the experiments given 

 under similar circumstances. 



The instrument with which their measures have been made 

 is altogether too bulky in such delicate researches ; for al- 

 though the bulb of a thermometer may be thrust into a pump- 

 kin flower or tulip with tolerable facility, yet the contact of 

 the circumambient air is not completely cut off by the shape 

 of the flower ; and if the fingers or any other contrivance 

 be used as a means of closing the corolla upon the thermo- 

 meter, the temperature of the new body complicates the 

 result. Even when introduced with all care, a bulk of mer- 

 cury or air of as many cubic lines as the flower has super- 

 ficial measure, in either case an imperfect conductor, can only 

 give a doubtful result. It is too large in most cases, and must 

 be confined to experiments upon a few scattered flowers ; nor 

 can it in any instance be made use of to obtain a set of mea- 

 sures over the whole plant ; most stems would be crushed in 

 attempting to introduce it ; and even if we succeeded so far, 

 the measure obtained must be imperfect, from the injury in- 

 flicted upon the plant and the small amount of mercury or air 

 in absolute contact. 



These considerations have induced me to make use of a 

 thermo-electric pair and the galvanometer as the most suitable 

 thermoscope. The pair consists of a tinned iron and copper 

 wire, each y^th of an inch in diameter, soldered together at one 

 extremity with tin for T \,th of an inch, and sharpened so as to 

 enter with slight force any part of a plant ; the wires used were 

 about nine inches long, and were passed through a large bung, 

 so that the fingers might not approach the junction, the cork 

 serving as anon-conducting handle, and being sufficiently re- 

 moved to hinder the possibility of producing a current of ther- 

 mo-electricity by radiation from the hand. The galvanometer 

 employed was the simple multiplier of Schweigger ; the axis 

 being suspended by a fibre of raw silk and bearing two needles 

 perfectly astatic, and also at the lower end a parallelogram 

 of tin-foil which was immersed in a vessel of water beneath 

 the galvanometer ; the object of this addition is to steady the 

 vibrations of the needles, as shown by Dr. Draper (Phil. 

 Journ.). The whole arrangement was covered by a glass 

 bell-jar, having a graduated arc pasted on the inside at an 

 appropriate height, which by moving the glass vessel can be 

 brought to any place so as to arrange the zero point with 

 great facility ; the upper needle also bore a fine wire standing 

 up at right angles from its extremity, which as the needle is 



B2 



