Radiant heat, and its conversion thereby into sound. 
301 
the beam, the decomposition of its vapour, a layer of the liquid iodide, of quadruple 
thickness, does not arrest the decomposition. The power, and the lack of power, to 
penetrate considerable depths is shared alike by the liquids and their vapours. Other, 
and still more subtle and penetrating illustrations of parallelism between liquid and 
vaporous absorption are mentioned in the Bakerian Lecture for 1864.'“ 
§. 3. Researches of Magnus. 
Prompted by the experiment of Grove, illustrating the chilling action of hydrogen, 
Magnus, in 1860, began an investigation on the power of gases to conduct heat.t His 
apparatus, traced in outline from his own plate, is shown in fig. 1, where A B is the 
Eig. 1. 
recipient for the gases, and C a flask containing water kept boiling by a current of 
steam. The bottom of C, which formed the top of A B, was the source of heat. A 
thermometer gf shielded by a cork or metal screen o o from the radiation of the source, 
was intended to receive and measure the heat transmitted by conduction. The recipient 
A B was mounted in a space surrounded by water of a constant temperature. The heating 
* Carbonic acid is one of the feeblest of the compound gases, as regards the radiation from solid bodies ; 
but, for the radiation from a carbonic oxide flame, it transcends all other gases in absorbent power. 
The action of aqueous vapour is also enhanced when it acts upon the rays emitted by a hydrogen flame. 
The enhancement extends to water. Curious reversals of diathermic position, when heat from different 
sources is employed, are moreover shown to occur simultaneously with liquids and vapours. 
t A Preliminary Note of this inquiry is published in the “ Bericht ” of the Berlin Academy for July 
30th, 1860. No measurements are given, but certain results are announced. The experiments were 
first published in PoggEkdoree’s Annalen for April, 1861. 
