TOL. XVIII,] PHILOSOPHICAL TRANSACTIONS. CS§ 



fleece of vaporous air, which once investing it, the vapour rises afterwards in 

 much less quantity : which was showed by the small quantity of water that was 

 lost in 24 hours time, when the air was very still from wind, in proportion to 

 what went off when there blew a strong gale, although the experiment was 

 made, as I said, in a place as close from the wind as could well be contrived. 

 For which reason I do not at all doubt, that had the experiment been made 

 where t'.ie wind had come freely, it would have carried away at least three times 

 as much as we found, without the assistance of the sun, which might perhaps 

 have doubled it. By the same experiment it likewise appears, that the evapo- 

 rations in May, June, July, and August, which are nearly equal, are about three 

 times as much as what evaporated in the four months of November, December, 

 January, and February, which are likewise nearly equal ; March and April an- 

 swering nearly to September and October. This fleece of vapour in still weather 

 hanging on the surface of the water, is the occasion of very strange appearances 

 by the refraction of the said vapours differing from that of the common air, 

 whereby every thing appears raised ; as houses like steeples, ships as on land 

 above the water, and the land raised, and as it were lifted from the sea, and 

 many times seeming to over-hang. And this may give a tolerable account of 

 what I have heard of seeing the cattle at high water-time in the Isle of Dogs 

 from Greenwich, when none are to be seen at low-water, (which some have 

 endeavoured to explain by supposing the Isle of Dogs to have been lifted by the 

 tide coming under it.) But the evaporous effluvia of water, having a greater 

 degree of refraction than the common air, may suffice to bring those beams 

 down to the eye, which when the water is retired, and the vapours subsided 

 with it, pass above, and consequently the objects seen at the one time may be 

 conceived to disappear at the other. 



^ Letter from Sir Dudley Cullum, to John Evelin, Esq. concerning a lately 

 invented Stove for preserving Plants in the Green House in JVinter. N° 2)2, 

 p. IQl- 



I send you an account of the success of your lately invented stove for a 

 Green House. I have pursued your directions in laying my pipes, made of cru- 

 cible earth, not too near the fire grate, viz. about \6 inches; and by making a 

 trench the whole length of my house, under the paving, for the air to issue 

 out and blow the fire, of a convenient breadth and depth, that is, 18 inches 

 both ways, covered with an arch of bricks, and at the other end of the trench 

 having a square iron plate answerable to that of my paving, which is 1 8 inches, 

 to take off" and put on, with a round hole at each corner, of about 3 inches 



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