rOJj. XVI.] PHILOSOPHICAL TKANSACTIONS. 366 



When these prunings had been tried on trees 20 feet high, the difference 

 of their increase was sensible the following summer ; but in 7 or 8 years time, 

 the difference is prodigious, the unpruned trees growing several times larger 

 than the pruned, both in body and branches. 



He has often observed also, that when the top branches would shoot out and 

 grow 2 feet or more in length, the lower branches would not shoot above 4 

 inches. And further, that in the branches of the Scotch fir, the joints above 

 the rings barked round would increase and grow much larger in 3 years, than 

 they would in 5 years if the said rings were not cut off. 



On considering these and several other observations and experiments, Mr. 

 Brotherton is of opinion, 1 . That the sap (most of it, if not all) ascends in 

 the vessels of the ligneous part of the tree, and not in the cortical part, nor 

 between the cortical and ligneous parts. — 2. That the increase and growth of a 

 tree in thickness is by the descent of the sap, and not by the ascent ; and if 

 there were no descent, a tree would increase but very little, if at all. — 3. That 

 there is a continual circulation of the sap all the summer season, and during 

 such time as the sap is stiring, and not a descent at Michaelmas only, as some 

 have held. 



To me it seems very probable, that the bodies of plants, as well as those of 

 moving animals, are nourished and increased by a double food ; the one an im- 

 pregnated water, and the other an impregnated air ; and that without a conve- 

 nient supply of these two, the vegetable cannot subsist, at least not increase. 

 These mutually mix and coalesce, and parts of the air conrert to water, and 

 parts of water convert to air. To this purpose all plants, as well as animals, 

 have a twofold kind of roots, one that branches and spreads into the earth, 

 and another that spreads and shoots into the air ; both kinds of roots serving to 

 receive and carry their proper nourishment to the body of the plant, and both 

 serve also to convey and carry off the useless recrements, useless I mean any 

 further within the body of the plant, though useful to it when they are sepa- 

 rated and without it, the one for seasoning the earth and water wherein it is 

 planted, and the other for seasoning and preparing the air, the method of 

 which I have elsewhere explained. 



Concerning the apparent Magnitude of the Sun and Moon, or the apparent Dis- 

 tance of two Stars, when near the Horizon, and when higher elevated. By 

 Win. Molyneux, Esq. N° 187, p. 314. 



It is well known, that the mean apparent magnitude of the moon is 30' 30* ; 

 ' we may take it at the round number 30', at a full moon in the middle of winter. 



