6 Professor Gardner on the Influence of the Dew-point 



Lest the deviation of the needle of the galvanometer should 

 be due to any other cause than a current produced by the 

 temperature of the plants, several experiments were made to 

 decide this point. The magnetic influence of the tinned iron, 

 the action of vegetable acids, friction, radiation from the per- 

 son or surrounding objects, were all examined, and it was 

 found, that under the precautions adopted, all these disturb- 

 ing causes were neutralized, so that all the measures given 

 are solely attributable to the presence of sensible heat in the plant . 



Where more than one measure is recorded, it was either 

 made upon different parts of the same plant, or at different 

 times upon different parts ; in the latter case, the time which 

 had elapsed between the measures is also recorded. 



Table A. 



June 8th, 1839. A vigorous group of Arum JValteri with 

 well-developed spathae, and several pounds of mud in situ. 



Thermometer 66° Fahr. Dew-point 54>°. Drying power 12°. 

 Clear. . 



Table B. 

 June 11th. Pastinaca sativa in flower, with adherent soil. 

 Thermometer 81° Fahr. Dew-point 66°. Drying power 15°. 

 Clear. 



