NATUUAL PHILOSOPHY. 143 



A few other experiments were tried, showing that soft lime and 

 hard lime have to be placed at different distances from the blow- 

 pipe nozzle to get the maximum amount of light from each. 

 Chemical composition even more than hardness varies the amount 

 of whiteness of the light. Magnesia cylinders were found to take 

 a longer time to heat to whiteness and a longer time to cool than 

 either lime or zirconia. Quartz rapidly vitrified under the flame, 

 and asbestos could not resist the intense heat. It requires time, 

 and repeated heatings and coolings, to test the permanency .of 

 zirconia under tlie oxyhydrogen flame to ascertain whether it 

 does away with the necessity for clock-work apparatus. The 

 piece used looked, at the close of the experiments, none the worse 

 for the operations it had undergone, and a native zircon crystal, 

 which,* on previous occasions, Messrs. Darker had occasionally 

 ignited under the oxyhydrogen blow-pipe, is now as hard as ever, 

 having shown no tendency to crumble, or soften, like lime, be- 

 neath atmospheric influences. The heat had produced in it traces 

 of vitrification, which could be seen only by the aid of a lens. 



MAGNESIA BLOCKS FOR THE LIME LIGHT. 



They are square prisms of about three-quarters inch base, and 

 five-eighths inch in height, of remarkably even texture, and nota- 

 ble density. Notwithstanding all that has been said in their 

 praise, they do not prove on trial to be by any means equal in 

 powers of resistance (when submitted to the oxyhydrogen flame) 

 to the average quality of lime. With a pressure of about 3 inches 

 of water at the jet, they are rapidly eaten away, and, moreover, 

 split by action of the heat. It is just possible that these specimens 

 have suftered some deterioration in their transit across the ocean, 

 though, considering their method of packing and the properties 

 of the material, this is hardly probable. 



Then one undoubted advantage seems to be their security from 

 injury on exposure to the air. In this respect, they have a marked 

 advantage over lime. Except, however, where exceedingly low 

 pressures are employed, their rapid destruction before the jet 

 more than compensates for the other advantage. 



THE ACTION OF LIGHT UPON VAPORS. 



This was a valuable paper by Professor A. Morren, read in 

 English by Mr. R. B. Ilayward, M.A., at the meeting of the Brit- 

 ish Association, " On the Chemical Reaction of Light, discovered 

 by Professor T3'ndall." Professor Morren said that he had repeated 

 Dr. TyndalPs celebrated experiments on the action of light upon 

 vapors in tubes, but that, living in the South of France, he used 

 the rays of the sun, instead of the light from the electric lamp. 

 His tubes, like those of Dr. Tyndall, were of glass, witli flat glass 

 ends, and glass stopcocks. Alter exhausting the air from the 

 tube, he permitted a mixture of absolutely pure dry hydrogen and 



