VOL. XXVI.] PHILOSOPHICAL TRANSACTIONS. 50Q 



From hence we may draw some remarks, that will be of use in practice, and 

 show that incisions may be successfully made on the cornea. 1. Incisions are 

 made on this part without any pain. 2. The orifices unite again without any 

 scar. 3. We find that plants of a discussive quality have a had effect, the 

 patient finding himself much worse after using a cataplasm made of cervil and 

 parsley : these plants, which are excellent in discussing extravasated blood in 

 the muscular parts, have bad effect when applied to the eye, by causing pain, 

 and rendering the sight more disturbed. When there is a considerable effusion 

 of blood in the eye, in couching a cataract, and no orifice is made in the cornea 

 to let it out, it may so alter the transparency of the vitreous humour, as to cause 

 a loss of sight ; which sometimes follows this operation. 



^n Experiment, showing that an Object may become Visible, in the Dark, through 

 such an Opaque Body as Pitch, while under the Circumstances of jittrition and 

 a Vacuum. By Mr. Fr. Hauksbee, F.R.S. N° 322, p. SQL 



This experiment affords a signal confirmation of another formerly made, and 

 differs only in the matter made use of. I before used sealing-wax, but now 

 made choice of pitch, which I employed as the sealing-wax, viz. I melted it in 

 a globe-glass, and kept it turning about until the larger half had got a pretty 

 thick lining of it, so that no ray of light could penetrate it. This globe I ex- 

 hausted of its contained air; then, being night, I put it on the engine to give 

 it motion ; where, after it had been turned a little while, with my hand on that 

 half lined with the pitch, I could very easily discover through the transparent 

 part, on the inner surface of the pitch, the very shape and lines of the hand 

 and fingers; for their most eminent parts, that touched the glass, appeared all 

 luminous: the other parts discovered themselves by the dark intervals they 

 made between the enlightened parts: and when the fingers were spread or 

 closed, it was very obvious to the sight. Now, after a small quantity of air 

 was admitted, the light disappeared from the inside of the lined part (but not 

 on the other,) which began to discover itself more and more on the outside ; 

 though even in vacuo there was always a light attended on the touch of those 

 parts that were most contiguous to the glass: but now a circle of light would 

 discover itself just on the edge of the pitch, which separated it from the trans- 

 parent part, as also another ring of light somewhat nearer the axis of the glass, 

 but both these appeared when the hand was applied to the under part ; for when 

 it was removed to the contrary, no such appearance ensued. The transparent 

 half of the glass was in all circumstances as in former experiments. When all 

 the air was admitted, the electricity of the glass in all its parts, the lined as 

 well as the transparent, performed much alike, the threads seeming to be at- 



