JOO PHILOSOPHICAL TRANSACTIONS, [anNO 1684. 



fected in the same manner as the air near the earth, by the vapours after sunset. 

 In the next place, this blindness comes gradually on him, like the vapours gra- 

 dually descending in the evening. Thirdly, the changes of the moon seem not 

 to have any effect on them, as the rising and fall of the vapours do not depend 

 on that planet. Fourthly, perhaps the crystalline and vitreous humours may be 

 so viscid, that, though the aqueous humour and tunica cornea be clear, they 

 cannot be dissipated. Fifthly, the blindness remains the same both in summer 

 and winter ; like as the vapours fall in all seasons, in a quantity sufHcient to 

 show the effect. 



Another correspondent gives it as his opinion, that as there is no observable 

 dimness in the person's eyes, the cause of the phenomenon is probably owing 

 to the disposition of the optic nerve; its little tubes, while filled with the solar 

 rays, easily admitting visible forms, as they are called; but when deprived of 

 them, they become flaccid, and unfit for vision. 



A Discourse on the Sepulchral Lamps of the Ancients, read before the Philoso- 

 phical Society of Oxford, May 7, l684. By Robert Plot, LL. D. Director 

 of Experiments to the said Society. N° l66, p. 8o6. 



At the last meeting, I showed that the downy part of the mineral called 

 linum asbestinum, earth-flax, or salamander's wool, would perform the office 

 of a wick tolerably well, it having burnt from about 9 in the morning, being 

 still supplied with oil, till about 4 in the afternoon, without sensible diminution, 

 yet it was objected that on other trials a friability had been found in it, which 

 argued some sort of consumption; and that allowing it invincible in the fire, 

 yet there might be some danger of its being clogged by the impurities of the 

 best oil that could be got, or any way prepared. To the first of which objections 

 it was then answered, that there was no such absolute necessity of making use 

 of that wool, but that another wick might be contrived, against which that ex- 

 ception could not lie; such as a metalline wire, especially of the best refined 

 gold, that will draw up oil as well as any other wick, and so make a perpetual 

 flame, provided it be supplied with a perpetual oil. In consequence, I tried a 

 parcel of wire made of annealed iron, of a suitable size for a wick, which could 

 not be made to succeed, nor have I much reason to think it will, after the most 

 mature deliberation, either in wire of silver or gold. If, therefore, it be neces- 

 sary that we must have a perpetual wick for making such sepulchral lamps as were 

 used by the ancients, I think we must stick to the first kind, made of linum 

 asbestinum, or salamander's wool ; which if it in any way can be supplied with 

 a perpetual oil, I hope you will not judge me far from effecting the matter. 



