RESIDUAL PHENOMENA. 



103 



fresh advances were quickly made in the knowledge of groups of com- 

 pound bodies. 



But there is another way in which the investigation of residual 

 phenomena may aid, and has largely aided, the advance of scientific 

 knowledge. 



Phenomena, regarded as residual, have not unfrequently been shown 

 to be completely explicable in terms of a known law ; and thus fresh 

 light has been thrown upon the modifying influence exerted on the ac- 

 tion of the law by the conditions under which the law acts. 



The orbit of Lexell's comet was accurately determined ; neverthe- 

 less, the comet failed to appear at the proper time. Here, surely, was 

 a phenomenon which could not be explained by the law of gravitation 

 alone : hypotheses, plausible and probable in themselves, were broached 

 to account for the apparently exceptional phenomenon. But subse- 

 quent investigation showed that that appearance of the comet, from 

 observations of which the orbit had been calculated, was due to the 

 disturbing influence of one of the members of the solar system (proba- 

 bly of Jupiter) whereby the comet had been dragged within the limits 

 of our vision, but that this visit to earthly spheres was altogether ab- 

 normal : the phenomenon presented by the visit of the comet was en- 

 tirely explicable in terms of the law of gravitation. 



What could be more opposed to our ordinary notions concerning 

 the effects of heat than the fact that water should be frozen in a red- 

 hot vessel ? But this phenomenon, apparently inexplicable in terms of 

 any known law, upon exact investigation finds demonstrable explana- 

 tion without recourse being had to the action of an unknown agent. 

 The experiment is carried out by pouring liquid sulphur dioxide a 

 liquid which boils at a temperature lower than that of the freezing- 

 point of water into a red-hot platinum crucible, immediately adding a 

 little water, and quickly turning out the ice which is produced. 



Experiment shows that when a liquid is suddenly brought into con- 

 tact with a highly heated smooth surface, vapor is evolved which sur- 

 rounds the mass of liquid as it were with a screen through which the 

 heat, radiated from the hot surface underneath, passes but slowly ; the 

 liquid thus rests upon a cushion of its own vapor, and does not touch 

 the hot surface beneath. The temperature of a mass of liquid in this 

 [spheroidal) condition is lower than that at which the liquid boils. 

 Now, as liquid sulphur dioxide boils at a temperature lower than that 

 at which water freezes, and as immediately the liquid touches the 

 heated platinum crucible it is partially vaporized, and the residual liquid 

 is then floated, so to speak, upon the stratum of gas so produced, it fol- 

 lows that, so long as this condition is maintained, the liquid contents of 

 the crucible are at a very low temperature; hence the temperature of 

 the water coming into contact with this cold liquid is greatly reduced, 

 and the water is frozen. 



Exact investigation of this phenomenon, therefore, adds much to 



