VOL. LXXXI.] PHILOSOPHICAL TRANSACTIONS. 117 



for producing easily such slips of it as, with a length of 8 inches, weigh only 

 about -rVth of a grain, and are thereby as quick as is convenient in other respects. 

 All those distinctive properties of the slip of whalebone seem to point out an hy- 

 groscopic substance fit for our common hygrometer. 



Description of the whalebone hygrometer. — Fig. 1, pi. 2, shows its form for 

 common use. The frame will be sufficiently known from the figure. The slip 

 of whalebone is represented by ab ; and at its end a is seen a sort of pincers, made 

 only of a flattened bent wire, tapering in the part that holds the slip, and pressed 

 by a sliding ring. The end b is fixed to a moveable bar c, which is moved by a 

 screw for adjusting at first the index. The end a of the slip is hooked to a thin 

 brass wire ; to the other end of which is also hooked a very thin silver gilt lamina, 

 having at that end pincers similar to those of the slip, and which is fixed by the 

 other end to the axis by a pin in a proper hole. The spring d, by which the slip 

 is stretched, is made of silver gilt wire; it acts on the slip as a weight of about 12 

 grains, and with this advantage over a weight (besides the avoiding some other 

 inconveniencies of this) that, in proportion as the slip is weakened in its lengthen- 

 ing by the penetration of moisture, the spring, by unbending at the same time, 

 loses a part of its power. The axis has very small pivois, the shoulders of which 

 are prevented from coming against the frame, by their ends being confined, 

 though freely, between the flat bearing of the heads of 2 screws, the front one 

 of which is seen near f. The section of that axis, of the size tliat belongs to a 

 slip of about 8 inches, is represented in fig. 2 ; the slip acts on the diameter aa, 

 and the spring on the smaller diameter bb. 



I have the honour, says Mr. De Luc, of presenting one of those instruments to 

 the Royal Society ; and, as it is very desirable that some hygrometer be added to 

 the other meteorological instruments usually observed, I wish this may deserve a 

 place in their observatory for that purpose. 



END OF THE EIGHTY-FIKST VOLUME OP THE ORIGINAL. 



/. On the Ring of Saturn, and the Rotation of the Fifth Satellite on its Axis. By 

 Wm. Herschel, LL.D., F.R.S. Fol. LXXXII. Anno 1792. p. 1. 



It is well known to astronomers that the ring of Saturn becomes alternately 

 enlightened on one of its sides, and that this change of illumination takes place 

 when the planet passes through the node of the ring. This happened in October 

 1789, when the southern plane, which had been in the dark for about 15 years, 

 became visible to us. 



In a former paper, (Phil. Trans, vol. 80, p. 4), where Dr. H. ventured to hint 



