240 PHYSICS. 



Spring lias continued his investigations on the welding of solid bodies 

 by pressure, and has now subjected more than eighty pulverized solids 

 to pressures in vacuo up to 30,000 atmospheres, varying at the same 

 time the temperature. All the crystalline bodies proved capable of 

 welding, and in the case of amorphous bodies, crystalline structure had 

 been developed in the block by the pressure. He classifies amorphous 

 bodies into two groups, one like wax and called ciroid, which weld easily, 

 the other like amorphous carbon, which do not weld, and hence called 

 aciroid. The facts observed do not essentially differ from those observed 

 when two drops of a liquid meet and unite. Hardness is a relative, 

 even a subjective, term. Even water may appear hard to certain insects, 

 and if our bodies were sufficiently heavy, the pavement would not bear 

 us. The change of prismatic to octohedral sulphur, of amorphous to 

 metallic phosphorus, by compression, the change of state of amorphous 

 bodies, the chemical action produced when the product has a less volume 

 than the constituents, all result in a denser form of matter. Whence the 

 conclusion that the particular state taken by matter is in relation to the 

 volume it is obliged to occupy under the action of external forces. #The 

 geological bearing of these facts is very evident. — {Nature, xxii, 350, 

 1880.) 



Eidout shows the surface tension of mercury by supporting a shallow 

 tray, 6 by 3 inches, on leveling screws, so inclined that the mercury" is 

 on the point of overflowing. If now the flow of the mercury be started, 

 it will draw the rest of the liquid after it. The mercury must be very 

 pure or it will leave a trail. — {Nature, xxii, 157, 1880.) 



Lechat has studied the forms produced when liquids are caused to 

 vibrate in vessels of rectangular section, and has compared the results 

 obtained with those required by theory. The vessels employed were 

 made of wood or glass, with walls a centimeter thick. The liquid was 

 vibrated by a bar of steel placed before an electro-magnet, which bar 

 automatically interrupted the current. To one end of a transverse rod 

 a stem was attached which could be adjusted to any point of the sur- 

 face. The nodal lines were very distinct, and the phenomena were very 

 striking, especially when projected on the screen. — {J. Phys., ix, 185, 

 June, 1880.) 



Sir William Thomson read a paper to the British Association on a sep- 

 tum permeable to water but not to air, and suggested its application to a 

 gauge for measuring depths. A small quantity of water in a caiiillary 

 tube, with both ends in air, acts like a perfectly air-tight plug against 

 difierence of pressure at its two ends equal to the hydrostatic pressure 

 corresponding to the height at which water stands in the same capillary 

 tube when it is held upright with one end under water and the other in 

 air. In the meeting, he used an Argand-lamp chimney which had a 

 finely- woven piece of cotton cloth tied over it. When dry, the water rose 

 easily when the uncovered end was immersed, as well as when the cov- 

 ered one was. But after wetting the cloth, it seemed perfectly air-tight 



