478 



Action of an Intermittent Beam of Heat, 8fc, [Feb. 24, 



III. " Further Experiments on the Action of an Intermittent 

 Beam of Radiant Heat on Gaseous Matter. Thermometric 

 Measurements." By J. Tyxdall, F.R.S. Received Feb- 

 ruary 21. 1881. 



In the concluding paragraph of the note communicated on the 10th 

 of January to the Royal Society these words occur : — " The vapours of 

 all compound liquids will, I doubt not, be found sonorous in the inter- 

 mittent beam." Since that time I have examined eighty different 

 liquids, both at the ordinary temperature of the air and at their boiling 

 temperatures, and have verified so far the- prediction just quoted. In 

 all cases I have obtained musical sounds — some feeble, some moderate, 

 and some exceedingly strong. I have, moreover, determined by ther- 

 mometric expansion the absorptions exerted by the vapours of more 

 than twenty of these liquids, and it is my intention to subject the whole 

 of them to this test. The harmony and mutual support exhibited by 

 two series of experiments, conducted in accordance with these two 

 diverse methods, are on the whole admirable. The investigation, how- 

 ever, is laborious, and many weeks must elapse before I am able to 

 submit it in extenso to the Royal Society. 



Tested by the thermometric method, my old experiments on aqueous 

 vapour again affirm their validity. A long and narrow glass tube, bent 

 into the form of a \J, was partially filled with coloured water. One 

 leg of the (J was connected with the recipient which contained the 

 gaseous substances submitted to experiment, while the other end was 

 left open to the air. Before permitting the beam to pass, the liquid 

 stood at the same level in both legs of the tube. Cleansing the reci- 

 pient thoroughly, and filling it with well-dried air, a powerful beam 

 was sent through it. There was no sensible expansion and consequently 

 no perceptible motion of the thermometric column. 



Air similarly dried was then passed over bibulous paper, moistened 

 by water of a temperature of 14° C. The modicum of vapour carried 

 forward at this temperature by the dried air, when smitten by the 

 beam, produced instantly a depression of 55 millims. in the leg of the 

 tube connected with the recipient, and an equal elevation in the other 

 leg. The difference of level in the two legs amounted, therefore, to 

 110 millims. rio trace of haze or sign of condensation could be 

 detected within the recipient. Its boundaries were as bright, and its 

 contents as free from turbidity, as when the dry air alone was 

 employed. 



With a conical tube of a certain size, stopped at its base by a trans- 

 parent plate of rocksalt, I have obtained a considerable intensification 

 of the sounds. Abandoning the ear-tube altogether, and filling the 



