[ 42 3 



to one third of the whole number.' The 

 preface contains a curious hiftory of the cli* 

 mate at Upfak and the progrefs of the feafons 

 through the whole year. From thefe obferva- 

 tions we learn, that the greateft degree of heat, in 

 the fummer of 1747, at Upfal^ was on the fecond 

 day of July^ when Celfius's thermometer ftood at 

 30 degrees above o ; that the greateft degree of 

 cold, on the 25th of January 1740, was 28 de-^ 

 grees below o« In this thermometer the freezing 

 point is o, and boiling water 100. From feven 

 years obfervations on the leafing of the oak, it 

 was found never to pufli before the 6th of 

 or to be retarded beyond the 2 2d. 



About this period it was, that LiNNiEus made a 

 remarkable difcovery, relating to the generation of 

 pearls in the river Pearl- Mufcle (My a. Margariiifera^ 

 Syft. 1 1 12.) This fhell-filli muft not be confounded 

 with what is called the Mother of Pearl Shelly as that 

 belongs to another genus, is a fea-fhell, and an 

 inhabitant of the warmer countries only. The 

 fliell-fifli in queftion is found in rivers^ in all 

 the northern parts of the world ; in Norway and 

 Sweden it abounds j it is found in the rivers of the 

 county of Tyrone in Ireland^ and in thofe of Done- 

 gall}, in Scotland^ the Don is faid to abound with 

 it and it is not unfrequent in the rivers of Eng- 

 land, This fifh will bear removal remarkably 

 well ; and it is faid, that in fome places they form 

 tefervoirs for the purpofe of keeping it, and 

 taking out the pearl, which, in a certain period 

 of time, will be again renewed. From obferva- 

 tions on the growth of thefc fhells, and the num* 



ber 



