244 On the Perspiration 
was made on the oceasion, though a well known and much 
esteemed astronomer, who had condescended to look over it, 
should have saved me from such an attack. Now nearly the 
same figure appears in the Linnean Transactions, and is acknow- 
ledged to be correct. I shal) just insert my flower to show how 
easy it is to be prejudiced by the name of the: presenter. | Fig. 
1 and 2. 
As I divided my book into several different Jaws, and that on 
Perspiration was one of the first, I shall once more introduce 
the subject, having much more new matter and new reasons to 
offer against it. I shall first notice that Hales, who was, I be- 
lieve, the first discoverer of perspiration in plants, lived at a time 
when the consideration of that apparent fact could scarcely ad- 
mit of the sort of examination it required. Since that time so 
great has been the alteradion established in our knowledge, that 
the decomposition of water, the acquaintance with the variety 
of gases, the condensation of the atmosphere, would alone de- 
mand a new arrangement. _ Now we know so much more of the 
regulation of the atmosphere, we are more capable of reducing 
the facts into natural phenomena, and bringing them nearer 
truth, Hales supposed that when a plant was covered it ex- 
uded a quantity of water. Indeed in the then state of know- 
ledge he had every reason to believe it so, since he found the 
water within the glass running down at the interior, and often 
the appearance of bubbles of water on the leaves. As to his 
drawing sap from the vegetable by means of glasses, he only 
drew that which was hourly rising from the earth in sap; but 
he neyer applied a microscope to know whether those bubbles 
were really water, or the rose leaf alone would have immediately 
satisfied him of his error : nor did he place under the glass another 
object, which would have pointed out to him his mistake, since 
he would have discovered that an almost dry sponge would give 
nearly as much water as the plant, a very diminutive quantity of 
which water could have proceeded from either, as the sponge 
would evaporate full as much as the plant. But this is very 
diferent from the loads of water, nineteen times more than a 
healthy man exudes in perspiration. Had this been really the case, 
no person could have sat under a tree without being completely 
wet. However, allow for the genera] exaggeration, and suppuse 
it only half the quantity, no microscope had been. directed to 
the plant, these apparent bubbles had never been examined, 
nor even touched with the finger, which would quickly discover 
that they were not uncovered bubbles of water, but a species of 
chemical glass: but this is not the only object of our research ; 
to discover from whence that water flows which appears under 
— ; = a glass 
