VOL. XXXVII.] PHILOSOPHICAL TRANSACTIONS. 511 



corresponding to each day of all the said years, will be found to be 50.1 6 

 inches. 



Therefore, by bare inspection into the table, it is easy to understand, that 

 the mean heights both of the barometer and thermometer, for each day of each 

 year, differ but a very few parts from the mean heights of the days, that arise 

 from these six taken collectedly. 



In the next place, S. Poleni proceeds to his observations on the magnetic de- 

 clinations; and these he discusses briefly. It is now well known, that at dif- 

 ferent hours of the same day, some small changes happen in the declination of 

 the magnetic needle; so that the same constant declination is not to be observed 

 for one entire day; but it varies sometimes a few minutes of a degree. It is 

 besides well known, that different needles, especially those touched by different 

 magnets, do not entirely exhibit the same declination, but sometimes vary 

 some few, (and but very few, when the needles are made by good workmen,) 

 minutes of a degree. Excepting therefore the very small variations, that easily 

 arise from these causes, S. Poleni, for these whole 6 years, observed the decli- 

 nation of the magnet, 13° towards the west. The compass he makes use of, 

 and on which he greatly depends, was made by Bernard Facinus, an artist well 

 skilled in these matters, and very diligent. The needle is 6 inclies long, and 

 weighs 32 grains. 



An Account of the Coccus Polonicus* By M. Breynius. N°421, p. 21 6. 



M. Breynius, after having briefly accounted for the two kinds of the cocci 

 tinctorii now in use, viz. that of Pliny gathered from the ilex, and the Ame- 

 rican coccus or cochineal, proceeds to give the natural history of the coccus po- 

 lonicus, which he calls radicum ; because it is chiefly found adhering to the 

 roots of the polygonum cocciferum, Kosmaczeh Polonis c. b. Kosmaczeh Pi- 

 losella Herbario Polon. This he takes to be the polygonum germanicum, 

 incanum, flore majore perenni Raii: of which he has given a print, with the 

 cocci, as they stick to the roots. 



The coccus, he says, is found sometimes single, sometimes more, even to 

 40 adhering to one plant, of different sizes, from a poppy seed to that of a 

 white pepper-corn. It is roundish, smooth, and of a purple violet colour, 

 and in a thin cuticle incloses a blood-red succus: one half or more of it is 

 covered with a rough, dark, brown crust, by which it adheres to the roots. 

 The countrymen gather it about Midsummer, and dry it with a slow Are in 

 earthen platters. 



• The insect here described is the coccus polonicus of Linnaeus. 



