1871.] Heat. 421 



their correlation will exhibit deformity." These instructions relating to the 

 use of the searcher have been quoted at full length, as some of the failures 

 in the use of the searcher have probably been caused by ignorance as to 

 the mode of its application, and as a natural consequence, observers disagree 

 as to its efficiency. The editor of the "Monthly Microscopical Journal" 

 justly remarks : — " There will, doubtless, be many cheap imitations, which, it 

 may be feared, will only caricature the properly constructed instrument, 

 which must be regarded as a new aid to microscopical research." It is unfor- 

 tunate that so elaborate a paper should give no constructive details to aid 

 opticians in manufacturing the instrument; the form of the lenses can only be 

 guessed at from the figures, no mention being made of their curves, or 

 the quality of glass employed. This is a great omission, which it is to 

 be hoped that Dr. Pigott will remedy by a future publication. Experiments 

 with a properly constructed searcher, in the hands of microscopists accus- 

 tomed to high power observations, are needed before the true value of 

 Dr. Pigott's invention can be ascertained. 



HEAT. 



The re-solidification of broken ice at temperatures above the freezing-point 

 has its parallel phenomena under like circumstances in the cases of many other 

 substances. Some of these are well-known, and at times exceedingly 

 troublesome' to workmen in certain manufacturing businesses where rapid 

 liquefaction is a desideratum, but they have not been noticed in any scientific 

 journal. Mr. C.W.Vincent has communicated to the "Chemical News" 

 some instances of these apparent parallels to regelation. Good black rosin, 

 free from turpentine, when subjected to pressure in a mould, or otherwise, at 

 ordinary temperatures, becomes completely pulverised, its particles showing 

 no cohesive power whatever. When the temperature of the mould is raised 

 considerably above the melting-point of rosin, on pressure being applied, a 

 different result ensues; the mass becomes at once solid to the core, the outside 

 alone showing signs of liquefaction. When rosin has to be melted for 

 manufacturing purposes, if even for a few minutes only the workmen neglect 

 to stir, the whole mass becomes completely solidified, and the liquefaction is 

 only carried on at the exterior of the mass, which, when pounded by his stirrer, 

 breaks up without giving the slightest preference to the previous lines of 

 fracture. Pitch, at melting temperatures, gives the same result as rosin, but 

 becomes viscid so much sooner, that though coagulation is readily affected, yet 

 the perfect junction of the broken pieces into a solid mass is not so readily 

 obtainable. The gums used in the manufacture of varnishes, such as dammar, 

 copal, anime, shellac, &c, give similar" results. Whilst being run down at 

 high temperatures, they settle together and cohere (if their surfaces be clean) 

 without the possibility of again separating them in the same places ; and this 

 while the exterior of the mass is rapidly melting into liquid of almost the 

 fluidity of oil. 



Aeronauts have frequently observed a phenomenon which they term as le 

 ballon fume sa pipe — that is to say, the gas the balloon is filled with issues from 

 the lower opening of the balloon in the form of a whitish smoke. Dr. de 

 Fonvielle supposes that this phenomenon is due to the cold produced by the 

 increase of the volume of the balloon while rising rapidly upwards. Indeed, 

 for a decrease of pressure of 1 millimetre per second of time, the increase of 

 volume is equivalent to that produced by an elevation of temperature of two 

 degrees for a height where the mean pressure would be 660 millimetres of 

 mercury. A similar phenomenon takes place in every instance of the rapid 

 rising of a mass of humid air, which, while becoming dilated, does as the 

 balloon and fume sa pipe — that is to say, leaves behind it, in the shape of more 

 or less dense cloud, the watery vapour which it contained previously in the 

 shape of a diaphanous invisible gas. 



A project for obtaining a larger amount of steam from a given quantity of 

 fuel has been patented by Mr. C. F. Varley and T. A. Rochussen. When 

 coal is burnt the solid coal is turned into gas, a large portion of heat becomes 



