152 SUDDEN INFLEX OF 



The heat fhou!d I" the pra^^ice of this lad procefs, care (hould be taken to 

 be applied l^at the oil gradually, and not to raife its temperature above 



fiiould not ^0 degrees oi" Reaumurs thermometer. (212 Fahrenheit) 



exceed So" This heat is Sufficient to effe6l the codion of the flour, and of 

 eaumur. ^^^^ mucofo-extradiive matter contained by the oil ; a greater 



degree of heat would colour the oil, and deprive it of the ap- 

 pearance moft favourable to its fale. 

 M. Curaudeau M. Curaudeau was led to this procefs by an obfervation, 



led to this pro- vvhlch every one may likewife make. It is well known that 



cefs by obierving 



%he reparation ^be fauce called melted butter, when too much boiled is fepa- 



of white fauce rated into two parts, one which is thick and occupies the bot- 



ftances when ^^"^ ^^ ^^^^ veffel, while the other part is clear and floats above 



too much done, (he firft : The lower fubftance is the cafeous part of the butter 



united to the flour that has been added to the fauce, and which 



the a6lion of the fire has Separated from the oil j The upper 



fubflance is the butter deprived of all foreign matter j and in 



this Hate it may be called purified butter. 



XI. 



On a peculiar FhBiiation of the River Dordogve, called the 

 Mafcaret. j?y yl/. Lagrave Sorbie *, 



JL HE peculiarmovementofthe waters of the River Dordogne, 

 The mafcaret which is called the Mafcaret^ takes place twice each day in the 

 when the waters ^""^'^^'" lime, zihcn the xvalers are low, which is an effential 

 are low. condition. A fimilar motion alfo takes place on the river Ama- 



zons according to the report of M. de la Condamine, when it is 

 The Pororoca of named the Poioroca; the fame is alfo perceived at the Orcades, 

 fimih!"to °r °^ ^^"^ ""'■''' "^^ Scotland, according this author : and M. 

 a like occurrence Sorbie has leen accounts in the publications of fome voyagers 



at the Orcades, of j^g likewife occuring in fome of the rivers of Hudfon's 

 4nd in the rivers , , ,,. . . ,.°^ . 



of Hudfonsbay, bay, and alio in theMiirifiipi. 



»!ifn;?r'^^ It is not furprifing (hat this phenomenon does not happen 



in all rivers ; it is not always feen even in the Dordogne. 

 From the moft exaft obfervation, if the fummer is not dry, 

 and that the waters are not low to a certain degree the Maf- 

 caret docs not appear, It rarely occurs in winter; it however 



RJiffiiripi. 



* Journal de Phyfique, LXI. 286. 



fonietlm^js 



