1813.] Philosophical Transactions, Part 11. 1812. 207 



greatest quan'tity of hydrogen gas that can be produced when 

 muriatic acid gas is elecirified over mercury amounts to about 

 ^th of the bulk of the original gas. 4. When the gas is elec- 

 trified in close vessels, both hydrogen and oxymuriatic acid gas 

 are evolved, probably in equal laulks, and the greatest amount of 

 both is ^'^th of the bulk of the original gas. 5. The presence of 

 hydrogen gas, mixed with the muriatic acid gas, prevents the 

 evolution of any more hydrogen gas by the action of electricity. 

 6. When oxygen and muriatic acid gas are electrified together, 

 w^ater is formed, and oxymuriatic acid gas evolved. In what 

 proportions it was found impossible to determine. 



XIV. Of the Attraction of such Solids as are terminated ly 

 < Planes \ and of Solids of greatest Attraction. By Thomas 



Knight, Esq. 



XV. Of the Penetration of a Hemisphere hy an indefinite 

 number (f ' equal and similar Cylinders. By Thomas Knight, Esq. 



XVI. On the Motions of the Tendrils of Plants. By Thomas 

 Andrew Knight, Esq. F.R.S.] Mr. Knight's observations were 

 made on the Virginia creeper (the ampelopsis quinqjieJoUa of 

 Michaux), the ivy, the common vine, and the pea. Tiie tendrils 

 uniformly receded from the light, and bent towards opake objects, 

 Mr, Knight explains this by supposing that the side of the tendril 

 acted on by light is elongated more than the other. This of 

 necessity occasions a bending from the light. The contact of the 

 tendril with any substance forces the nutritive juices of the 

 tendril towards the side farther remote from the opake body. 

 Hence a farther elongation of that side, and a consequent twist- 

 ing of the tendril round the opake body. 



XVII. Observations on the Measurement, of Three Degrees of 

 the Meridian, conducted in England by Lieut. -Col. William 

 Mudge. By Don Joseph Rodriguez.] The determination of the 

 figure of the earth has at all times attracted the curiosity of man- 

 kind ; attempts to ascertain which were even made by the an- 

 cients : but our ignorance of their measures makes it impossible 

 for us to draw any information from these attempts. Buygens 

 and Newton were the first who reduced to the known laws of 

 mechanics the principles on which the figure of the earth should 

 be determined. The Academy of Sciences of Paris had tlie 

 glory of first applying these principles to practice, by their cele- 

 brated measurements, performed in Peru, Lapland, and France, 

 The conclusions of Newton and Huygens were verified by these 

 measurements, and it was concluded that the figure of the earth 

 was a spheroid flat at the poles, and jutting out towards the 

 equator. Of late several new measurements have been made 

 with more accurate instruments, greater skill, and more care if 

 possible than the former ones. The French philosophers, at the 

 commencement of the Revolution, measured the whole length of 



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