;£f34 PHILOSOPHICAL TRANSACTIONS. [aNNO 1705. 



inch, although the quantities fired were equal ; but still the undulations in- 

 creased, and the explosions manifestly did so too: till at last the receiver seemed 

 to be in great danger of being blown up by a single quantity ; the undulations 

 of the mercury being then augmented to 6 or 7 inches. Now 26 quantities or 

 32 grains having been fired upon the iron, and the mercury in the gauge fallen to 

 12f, I carefully observed the gauge, which in 7 minutes had ascended 2| inches, 

 the next 3 minutes it rose but 1-^- inch; and so less successively every 5 minutes, 

 so that in an hour and 17 miimtes it had attained only to 21 inches, the iron 

 not being quite cold. At 9 the same night I observed the gauge, and found 

 the mercury elevated to 224- inches, precisely: next morning at 9 it had at- 

 tained to 221; and so continued all that day, the iron then being reduced to 

 the temperature of the outward air. So that from 12^ to 22^- seems to be the 

 weight or spring of heat equal to about 4- of an atmosphere of air, which would 

 press the mercury upon the upper part of the gauge, but equal to such a degree 

 of heat as was then contained in the receiver, when the gauge was fallen to 12f : 

 the remaining space, from 224- to 29^, is supposed to be supplied with factitious 

 air, and answers to about ^ part of the whole contents of the receiver, which 

 was equal to 254^ ounces of common water, allowing for the iron and pedestal. 

 This air, produced from gunpowder, I find to be actuated by heat and cold as 

 common air: for, holding my warm hands upon the receiver, the mercury in the 

 gauge would immediately descend, and rise again when reduced to the tempera- 

 ture of the outward air. This I repeated several times, with the like success. 

 What further occurs in this experiment is, why the explosions of the like quan- 

 tities of gunpowder should be greater when resisted by air, than in vacuo, where 

 nothing seems to hinder the extension of their flame. 



Georg. Joseph. Camelli, De Plantis Philippensibus scandenlibus ; Pars Tertia, 

 Ad Jacobum Petiver, S. R. S. nuper transmissa. N° 295, p. 1 8O9. 

 A continuation of the catalogue of climbing plants, growing in the Philip- 

 pine Isles. 



ji Universal Spherico Catoptric Theorem, By Mr, Humphry Ditton, N° 295, 

 p. 1810, Translated from the Latin, 



The finding the foci, both in dioptrics and catoptrics, easily follows from the 

 calculation for the caustic curves. For nothing more is requisite, than to know 

 the locus in which the radius (perpendicular to the curve, either reflecting or re- 

 fracting) is a tangent to the diacaustic or catacaustic curve. Concerning which 

 method, there may be consulted Mr. Hays' book oji Fluxions, lately published. 



