318 PHILOSOPHICAL TRANSACTIONS. [aNNO 1793. 



that the inside, together with the lower part of the thermometer, may become 

 totally covered when cooled; which coating may easily be removed by means of 

 a little oil of turpentine, or any other essential oil, all of which dissolve wax 

 very readily. 



XV. Extract of a Letter from Sir Charles Blagden, Knt., Sec. R. S., giving 

 some Account of the Tides at Naples. Dated Rome, March 30, 1793. p. l68. 



I took some pains at Naples to get information about the state of the tides, 

 but could learn nothing satisfactory. The quantity of rise and fall is so little, 

 that unless the sea be very calm, it is impossible to make a good observation. 

 One of the best places for ascertaining the phenomena would be at what they 

 call the river Styx, which is a narrow communication between the Porto di 

 Miseno and the the Mare Morto. Here I learned very distinctly that the water 

 sometimes ran in, and sometimes out, but could not get the times; when I was 

 there it was running out. The best observation I had was on the 2d of March, 

 when it appeared to be high water at Naples about 1 ] in the forenoon, and low 

 water between 5 and 6 in the afternoon; with a difference of pretty exactly 1 

 foot in the height. The wind blew the same way all the time, and the sea was 

 very little agitated. On the preceding day the water had sunk an inch or 2 lower. 

 From this observation, as well as some others less accurate, I concluded the time 

 of high water at full and change to be between 9 and 10 o'clock, in the Bay of 

 Naples. 



XFl. Observations on Vision. By Air. Thomas Young, p. 169, 

 It is well known that the eye, when not acted on by any exertion of the mind, 

 conveys a distinct impression of those objects only which are situated at a certain 

 distance from itself; that this distance is different in different persons, and that 

 the eye can, by the volition of the mind, be accommodated to view other objects 

 at a much less distance: but how this accommodation is effected, has long been 

 a matter of dispute, and has not yet been satisfactorily explained. It is equally 

 true, though not commonly observed, that no exertion of the mind can accom- 

 modate the eye to view objects at a distance greater than that of indolent vision, 

 as may easily be experienced by any person to whom this distance of indolent 

 vision is less than infinite. The principal parts of the eye, and of its apperti- 

 nances, have been described by various authors. Winslow is generally very ac- 

 curate; but Albinus, in Musschenbroek's Introductio, has represented several 

 particulars more correctly. I shall suppose their account complete, says Mr. Y., 

 except where I mention or delineate the contrary. 



The first theory that I find of the arcommodation of the eye, is Kepler's, He 

 supposes the ciliary processes to contract the diameter of the eye, and lengthen 



