VOL. XLIl.] PHILOSOPHfCAL TRANSACTIONS. 579 



in which the quicksilver rose the highest, and often a full inch higher than in 

 N° I, was made of the whitest glass; this shows a remarkahie phosphoric light, 

 and has a wooden cistern ; but its heights change slower than any other, and 

 is N° 7 in the same class. N" 3 is a diagonal one, with a single bend, and a 

 bent glass cistern. N° 4 is Bernoulli's, the tube of which, is to the cylinder 

 fastened above, as 1 to 8. N° 5 is Huygens's. N° f) is another diagonal one, 

 but with a double bend, one of which is received by that part of the tube to 

 which the scale is applied, intercepting an angle of about 25°, with the per- 

 pendicular part of the tube, in the double angle of which, because of the nar- 

 rower width of the tube, the quicksilver must be greatly retarded in its ascent 

 and descent. 



The barometers in the 2d class have their lubes of a different kind of glass; 

 which when melted at a lamp, partly loses its transparency, and its surface be- 

 comes covered with very small scales. In these tubes the quicksilver rises the 

 highest in the upright and simple barometers, excepting only that which pro- 

 duces the phosphorus. 



The 3d class contains those barometers having very white glass tubes, that 

 suffer no alteration from the fire, and are all straight and simple. The differences 

 among these amount only to l-J- line; and their greatest height only exceeds the 

 least of the others by about 4 lines. 



Are we therefore, asks M. Hollman, to seek for the cause of this difference 

 in the diversity of the glass tubes? Is not the surface of one more rough and 

 uneven than that of another, and does it not therefore more or less resist the 

 ascent of the quicksilver by its friction? or is it from any other cause?* 



Class i. Baromer used July 27 and Aug. 12. Class hi. 10 Barometers made Aug. 12, the 



N° Aperture Height first 5 having no annexed cisterns, but the last 5 



1 \ line 27 inch. 1 1 lin. having bent glass cisterns. 



2 i 28 1 N" Aperture Height 



3 i 27 11 1 I line 27 iuch.ll^lin. 



4 28 4 2 I , 



5 28 . . . 5 3 IJ 



6 i 28 ... . 7i 4 2J 



7 i 28.... 9 5 \i 



Class ii. 8 Barometers new made July 27. 6 1\ 



1 2 28.... li 7 i 



2 2 28 4 8 1 



3 If 28 4 9 li 



4 1| 28 2i 10 i 



5 l| 28 . . . 2 Now, since difterent barometers have such'dit- 



6 1-1 28 ... . 2 ferent heights, M. H. concludes we ought to think 



7 1 28 ... . 2 about harmonic barometers as earnestly as about 



8 I 28 ... . 4 thermometers, before we can accurately collect 



* Probably the diversity and smallness of the tubes have a great effect on the heights. 



4 e2 



