Polytechnic Association Proceedings. 623 



of mica giving it great advantages over glass. After being heated, 

 mica loses most of its flexibility, but it then makes a beautful ma- 

 terial for inlaying work. A pretty efiect is obtained by scattering 

 small fragments of mica on freshly poured sheets of gelatine, and 

 varnishing it with a dark solution of gelatine. Finely ground 

 mica, mixed with a solution of gum arable, may be used for a 

 silver ink. 



SPECIFIC HEAT OF SOILS. 



Pfraunder, in his investigations concerning the specific heat of 

 soils, during which he determined that of seventeen diflereut soils, 

 has noticed that soils free from humus have the lowest specific 

 heat, whether they consist of lime or sand. The richer a soil in 

 humus, the higher is the specific heat. Thus peat was found to 

 have 0.507, and a soil very rich in hnmus gave 0.4142, while that 

 of calcite and quartz is only twenty and nineteen. Loamy soils 

 must have a high specific heat, owing to the presence of water. 

 These facts are important to the agriculturist, since a plant sensitive 

 to the changes of temperature would not grow well on soils of low 

 specific heat. 



CANDLEING EGOS. 



This operation of looking through an egg, by means of a candle 

 placed behind it, is called candleing an egg, by poulterers, who 

 have taken advantage of its transparency in order to ascertain its 

 soundness. From a mere trade practice, it has risen to the dignity 

 of a scientific manipulation, and more perfect apparatus has been 

 made for detecting the changes going on within the egg at diflferent 

 periods of incubation; also for assisting in researches on the forma- 

 tion of monstrosities, by coating portions of the shell. Carbon- 

 nier's apparatus consisted of a hollow cylinder, in the center of 

 which was a powerful light. The Bulletin de la Sodete cTAccli' 

 matation has lately published the description of another plan, 

 which consists in a screen, sliding in a groove cut in a block, used 

 as a pedestal. This screen, which is of wood, has a longitudinal 

 slit in a vertical direction, behind which is a lamp, the light of 

 which is imprisoned, so as only to fall on the egg placed in front 

 of the slit. In large egg-hatching establishments eggs are gene- 

 rally candled on the tenth day of incubation. 



A TREMBLINa PLANT. 



Besides the class of sensitive plants which display a kind of irri- 

 tability at the approach of some extraneous body, there is another 



