404 PHILOSOPHICAL TRANSACTIONS. [aNNO 1773. 



from the injuries of the weather. As soon as the warm weather in the spring 

 begins to be felt, the buds open, and their coats, which then become useless, 

 drop off, and give place to the productions which they contained and preserved. 

 Immediately after this, the blossoms, flowers, and fruits make their appearance. 

 This is the usual operation : but in the case before us, nature was, as it were, 

 surprized by art; what she should not have done till spring, she did in the 

 winter, because the heat of the hot-house produced that expansion, which, 

 according to the natural course, ought to have been effected by the rays of the 

 sun darting less obliquely than before on the horizon. There is no doubt but 

 it is to heat, either natural or artificial, that this expansion is owing; and 

 the experiment proves that it is only in that part of the tree, which is exposed 

 to the effect of heat, that the sap, which in every other part remains torpid and 

 inactive, is put into motion, and produces vegetation. From this it appears, 

 that the vegetable economy is different from the animal, and that those v/ho 

 endeavoured to establish the circulation in both, carried their analogy too far. 



This fact, now established, furnishes a good reason why in the tapping of the 

 maple and sugar birch trees, so much liquor runs out on one side, and none at 

 all on the other. It is well known that, if during the time of a frost, or a 

 summer's day, towards noon, you bore a hole on the side of the maple tree 

 exposed to the south, you will get a great quantity of liquor from it; and that if 

 you bore the north side at the same time, you will not get a drop. The cause 

 of this evidently appears from what has been said. We likewise see why trees 

 exposed to the south lose a great many of their branches, and sometimes die 

 altogether, in the course of a severe winter; while trees of the same sort, but 

 placed to the north, or in some other exposition, will stand the hardest frosts. 

 This is particularly remarkable in the evergreens, whose resinous and oily sap 

 being liquefied by the heat of the sun, tjie tree cannot escape suffering a great 

 deal, whenever it is surprized in that state by the night frosts. Those observers 

 who attend to this, and know how well pines, firs, and bays succeed, when 

 planted on the back of mountains exposed to the north, will take care not to 

 place such kind of trees in a southern aspect, in hopes of their succeeding 

 better by it. 



XF^I. Actual Fire and Detonation produced by the Contact of Tin-foil, with the 

 Salt composed of Copper and the Nitrous Acid. By B. Higgins, M. D., 

 p. 137. 



Several pieces of thin sheet copper, placed vertically, and at a small distance 

 from each other, in the strong nitrous acid diluted with half its quantity, or 

 more, of water, and suffered to remain in a close vessel, till the acid is saturated, 

 afford a crystalline bluish green salt, which is to be separated from the 

 undissolved copper and the superfluent green liquor, and kept in a well corked 



