178 On the Rate of Cloch. 



and motion will prevent congelation even in water, if not already 

 too near the freezing point. But observing tliat the snow passed 

 off in breadth in ])roportion to the .sj)reading- and shading of the 

 branches ; I fixed a long stick in tlie ground, and tied an um- 

 brella to it, which should, whtn spreading, be about six or seven 

 feet from the earth. It was then going to snow; and when it 

 wae already pretty deep round the stick, I expanded the umbrella, 

 and before the next morning, the whole extent ^f the circle of 

 the parasole was tofally melted before nine o'clock. It could 

 not therefore be any effect of the roots of plants that caused the 

 snow to dissolve ; but was it not rather the dews and vapours 

 falling and sinking among the dead leaves, putrid vegetable 

 matter, or calcareous earth, which became nitrate of potash or 

 saltpetre, and of course increased the cold, and preserved the 

 congelation of the rest of the snow? Many other trials and 

 experiments have since that time confirmed my cojwiction of its 

 propriety ; though not of consequence enough to be suhnilted 

 to the reader. I cannot help thinking that we are little aware 

 how many juices, and various liquids and compomids, are be- 

 stowed on us by the atmosphere. The hairs of the plants make 

 that subject most visible, though they may, like the salts afore- 

 mentioned, not descend to us in a perfect state ; vet they cerr- 

 tainly (with tlie liquid already in the hairs, or rising immediately 

 after m them) receive affinities which produce most of the scents 

 and juices that form our fragrant oils and resins. 

 I am, sir, 



Your obliged servant, 

 Sherwood, Feb. 3, 1815. AgnBS IbBETSON. 



XXXI. 071 the Rate 'f going of iwo Clocks, with Remarks 

 on Harris's Pendulum Clock erected in 1611. By Mr^ 

 Thomas Reid. 



To Mr. Tilhch. 



Sir, — JL HE circumstance of two clocks keeping the same time 

 &o closely together, and that for periods of considerable lengths 

 of time, appearing extraordinary and imexpected to me, is the 

 reason why I have transmitted the case to you ; and should you 

 deem it worthy an insertion in your valuable Journal, it is at 

 your service. 



Both the clocks were going in an imperfect state, and were 

 intended for further improvement: but their assuming the 

 appearance of keeping so near together, made me delay the 

 taking them down to make any alterations, till I saw how long 

 they would continue to do so; which Uiey did for such a length 



