2-.8 Ptailiiir Motions of Comphor and atler Bodies. 



tlie water, but cannot continue their motion becaufe the film which they form at the fur- 

 I'.ice of the water is not diiripatcd in the atmofpbere. From this lad obfervation the Author 

 ilctluces this confi;quence, that volatility and the odorant property are not qualities ncccflary 

 (•■ produce ihefe rotations. Volatility is merely necclTary for tl\cir continuation. 



At the end of his memoir, the Author fpeaks of certain other motions obfcrvcd in na- 

 ture, which, by tlie mechanifm of their caufe, arc in fomc refpe£l analogous with the motions 

 of oily bodies at the furface of water. In bodies brought near the tire, the humidity re- 

 tires always to the extremities mod remote from the fire itfclf ; becaufc the vapour wjiich 

 is difenpaged from the part mod heated repels the reft in the oppolite dire£lion. So like- 

 wife drops of water, thrown on an ignited plate of metal, remain, and are agitated in the 

 form of a fpherc ; becaufe the vapour which is produced by the conta£t of the plate agi- 

 tates them, and docs not permit tliem to touch the metal. By the fame principle, it is 

 very cafy to explain tiie motions of the tremella defcribed by danfon and Corti, which had 

 inclined fome naturalifts to rank this byfl'us in an intermediate clafs between plants and 

 vegetables. The tremella is a mafs of very minute fibres, which being fufpended in tlic 

 water muft be fenfible to the flightcfl imprefiion. It is at prefent known, that pl.mts, when 

 c.xpofed to light, decompofe tlie water in their veflcls, of which they feize the hydrogcnc, 

 and extrude the oxigenein the form of gas, by an operation nearly the reverfe of animal 

 refpiration. If from one of the fibres of the tremella the gas ilTues on one fide, the fibre 

 itfjlf muft bend toward the oppofite part. If, as in large trees, the gas ifTues from the tre- 

 mella in the greateft quantity from the fide of the plant which is oppofite the light, the 

 tremella muft be repelled towards the fource oT the light itfelf, to which it always tends 

 when included in an opake veflel, into which the light enters through a hole. It is not 

 therefore necefl"ary for the explanation of this faft, either that we fliould fuppofe any de- 

 gree c»f animality in the plant, or attraction at a diftance between the oxigene and the 

 light. In the fame manner, the gas which is abundantly produced by the light of the day, 

 becomes accumul.tted between the fibres of the tremella, and floats it to the furface of the 

 water. The Author takes occafion to exprefs his acknowledgment to Citizen Fourcrov, 

 who afforded him the means of repeating the experiments in his laboratory, and who, by 

 liis excellent Icffons, informed him of the facbs nswly difcovered fince the communication 

 between his country and France had been unfortunately interrupted. 



ABDiriOyS to the f reading MeMOIR- In a Letter frsm the AUTHOR to Citizen FoURCROV. 



Citizen, 

 AS 1 underftand that an extraifl of my memoir upon the feflion of camphor at the furface 

 of water is intended to be printed, I requeft you will add tht following fads and reflexions: 



1. Dry camphor is very perceptibly volatilized under the weight of the atmofphere, at 

 the soth degree of Reaumur (145 Fahrenheit). It melts at the 120th degree (30 J Fahren- 

 heit), and its volatilization is then extremely rapid. In the Torricellian vacuum it rifes 

 even at the ordinary temperature of the atmofphere. This vapour has very little elafticity. 

 It cryftallizes along the fides of the tube. 



2. A column of camphor is cut afunder much more fpeedily at the furface of boiling 



than 



