tjjjlorlcal Sketch of the' Uoydl Society of London, ^^ 



that the tvater on which the fubftance with which they mean 

 to make their experiments is thrown, may have a large iur- 

 face, and the experiment will be decifive when it is performed 

 in a veflel into which the water flows and runs out, or in a 

 river or pond. 



If the experiment be made in a velTel filled with watery 

 oily impurities may eafily adhere to the fides of it, and thus 

 prevent the cftedl, as they will occupy the furface of the 

 water. 



Care mud be taken alfo that no oily fubftance, of what- 

 ever nature, may have been previoufly adhering to the veflel ; 

 for, in that cafe, the experiment would fail. 



The evaporation of the body may alio occafion decep- 

 tion. I have mvielf obferved, that when the hand is rubbed 

 under the armpits, over the forehead, or on any other part 

 of the body from which more oily evaporation proceeds than 

 from others, and if a piece of earth be taken in this hand and 

 placed on the water, an extenfive movement immediately 

 takes place. The fame thing may happen, if the fubftance 

 with which the experiment is made be held a long time in 

 the hand. It is therefore necefl'ary to wafli the hands, and, 

 after thev have been well dried, to proceed to the experiment 

 by throvving the fubftance on the water from a fmall fpoon. 

 It may thence be readily conceived what errors may ariie it" 

 all thefe precautionary rules are not obferved. 



V. HiJIorical Sketch of the Inflilut'ion and Progrefs of tk& 

 Royal Society of London, 



B, 



►ELTEF in the influence of the ft:ars on the fortune and 

 character of man, together with the attention always un- 

 avoidably given to the meafurement of time, prefervcd fome 

 knowledge of aflronomy among our anceliors even in tlie 

 darkeft ages of modern Europe, and rendered it one of the lirlt 

 objeds of zealous ftudy at the sera of the general revival of 

 learning and fcience. The alchemical dream of the convcrti- 

 bilitv of all bafer metals into gold, engaged many an enthufiaft 

 and many an impoltor in experiments in chcniiftry, from the 

 carlieft period in modern hiflory from which we have any 

 informaiion of the purfuits of the inquifitivc and the learnccf, 

 'i'he ufes of common life, and the redoration of this part of 

 the fcience of the antients, encouraged and advanced the 

 liudy of mechanics even in the fifteenth and fixteenth cen- 

 turies. No other bjanch of phyfical fcience but thcfe ihreo 



had 



