1822.] Formation of Ice in the Beds of Rivers, 189 



met'dl allowing of a closer, though still partial contact with the 

 bounding atmosphere, is thus brought to a state more favourable 

 for exciting energetic pulsations. On the same principle, a thin' 

 covering of muslin, or even of flannel, instead of retarding the 

 escape of heat, as a priori we should suppose, does actually 

 favour its more rapid discharge. 



The NW, wind probably acts by its greater degree of cold, 

 causing (at least until the temperature of the entire mass is 

 reduced to 39) a constant precipitation of chilled particles from 

 the surface to the bed of the river. 



How the rapidity of the currents can hasten the effect, it is 

 difficult to say ; unless on the same principle that a strong 

 breeze accelerates refrigeration in atmospheric air, so in like 

 'manner the rapid current affording a constant supply of water at 

 a lower temperature may cool down the bed of the river with 

 greater rapidity, and thus bring it to a condition more favourable 

 for the production of this icy crust. 



It will in all probability be objected to the suggestions I have 

 here thrown out, that they are in direct opposition to the obser- 

 vations of Prof. Leshe, who asserts, that when the cannister, 

 reflector, and difterential thermometer, were plunged into water, 

 that no radiation could be observed, and hence this ingenious 

 philosopher concludes, that no radiation will take place, except 

 when the radiating body is surrounded by an elastic medium. I 

 may remark, how^ever, that the experiments which he adduces 

 in support of this opinion are by no means decisive of the point. 

 Substances, as Dr. Thomson very accurately remarks, cool so 

 rapidly when plunged into water that there is hardly time for the 

 difterential thermometer to be affected ; besides that, the heat 

 could scarcely accumulate in the focal ball in such quantity as 

 to occasion a sensible rise. 



Moreover, I can see no reason whatever why radiant caloric 

 should not pass through water^ as well as air. They are both 

 fluids ; they receive and transmit slow communicating caloric 

 in a precisely similar way ; namely, by a constant recession or 

 migration of heated particles : they agree in many of their phy- 

 sical and chemical properties, such as great freedom of motion 

 among their particles, extensive solvent power, elasticity, &c. 

 What is there then I would ask in the constitution of water that 

 should incapacitate it for the transmission of radiant caloric ? 

 Moreover, if not transmitted through this fluid, what then 

 becomes of it ? Is it converted into slow communicating caloric ? 

 This would be asserting their identity, a point about which I 

 may remark philosophers are by no means agreed. But admit- 

 ting the fact, it appears to me that such a conclusion would be 

 rather favourable than otherwise to the hypothesis I have ven- 

 tured to advance ; for if slow communicating caloric be capable 

 of direct transmission through fluids, and of this, the experi- 



* There is no doubt that radiant heat can pass through water : the question is, whe- 

 ther it can commence its radiation in water. — Ed. » 



