Covimuiilcathn from Dr. 'M'dchUl. i^^ 



this kind, which were atlcnded with the widied-for fiicccf:^ 

 as when he employed oil : we know alfo, from the inform- 

 ation of Scheldeniing, that the whirlpool of the Maelftrom 

 has been moderated by throwing pieces of wood into it. 



To form a decifive opinion refpefting the utility of thefe 

 means, it would be necelTary to make experiments upon a 

 large fcale. At prefent oil appears to me to deferve the pre- 

 ference, as it produces the effe6l, not only by its being a 

 lighter body, but alfo by its fluidity and toughnefs : bcfides, 

 it poffeffes this advantage, that a fmall quantity of it is fuffi- 

 cient to fpread over a confidcrable furface of water. 



It has been objeiRed againll this ui'e of oil, that the calm- 

 nefs produced by it has been obferved to be only of fliort 

 duration, and that the fea afterwards red,)ublcs its fury: 

 alfo, that a veflel which follows a flap failing through water 

 calmed by the above means, is expofed to fo much greater 

 danger; but of this circumftance no teftimony of fufHcient 

 authority has been adduced *. 



II. Communication from Dr. Mitchill, of Nezu-Yori^ 

 Jbewing the Utility of conJlrnEting the Houfcs and paving, 

 the Streets of Cities with calcareous in preference to ftli~ 

 ceous and argillaceous Materials. 



I 



SIR, Neiv-Yorh, Ju?ie 6i\\, i'](^g. 



F you think the inclofpd letter of any importance, I wifh 

 you would iafert it in the Philofophical Magazine. It is fo 



'* Tranfaflions of the Society of Manchefter, Vol. II. Achard's 

 Sammlung pby/ikalifcher unci cbemijcher Aljbaiidlungen, Vol. I. Berlin, 

 1784, p. 83. Ejfay fur tes moyens dc diminuer les dangers dc la mer par 

 t aff'ufion de I'bui/e, du gouJron, on de quclque autre viatlere foiiuiif, par. 

 M. dc Helyveld, Amft. 1776. Letters and Papers on Philofophical Sub- 

 jects, by Franklin, p. 438, Miijlir de Cflt-bralii old aqua- Jupajufi ef- 

 JcSiibiii optuii et mccbaiikis, 177&. — The laft work trciits more on the 

 jeflimony of the Ancients, than on the experiments that have been made. 



p8rfc(J\ly 



