144 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



meter. This product in fact, which for perfect gases is con- 

 stant, varied rapidly in the case of air. The deviations from 

 the law of Mariotte for rarefied air are contrary to those 

 observed by Regnault for compressed air. In fact, the prod- 

 uct increases when the pressure increases, and diminishes 

 when the pressure diminishes. These discordances are far 

 larger than the possible errors of observation. 



AIR PUSHED IN FRONT OF A PROJECTILE. 



In investigating the various phenomena attending the im- 

 pact of projectiles, Busch has studied the question as to 

 whether a sphere falling into a fluid drives air before it, or 

 whether the air is simj^ly inclosed by the water as it comes 

 together behind the sphere. The simple apparatus em- 

 ployed by him to study the question consists of a cylindri- 

 cal vessel full of water in which a j^late is hung having in 

 the centre an opening so large that the sphere falling 

 through the water will be caught by it. His experiments 

 show that in the case of bodies falling with a very small liv- 

 ing force, the air above the water has time to be comj^letely 

 pushed aside by the falling projectile. But that if the living- 

 force of the body is increased slightly to a certain limit, it 

 no longer becomes possible for the air to be entirely pushed 

 aside ; but that a certain amount is pushed by the sphere 

 forward, and the quantity of air so driven on increases 

 with the increase in the living force to precisely the degree 

 required by the measurement of Magnus, upon the quantity 

 of air carried with the projectile into the water. If we in- 

 crease the resistance of the fluid by taking some more viscid 

 fluid than water, such as glycerine or oil, it is found that a 

 greater living force is required in order to carry the air in 

 front of the projectile into the fluid. Even in the case of a 

 shot penetrating a solid body, such as a thin sheet of India 

 rubber stretched over the opening in the plate, a certain 

 quantity of air is driven through in front of the ball. Ver- 

 handl. Naturhist. Yereins^ Bonn^ XXXI., 251. 



ON THE PROPULSION OF AIR BY A JET OF AIR OR VAPOR. 



An interesting and j^ractically valuable series of experi- 

 ments has been made by Romilly on certain phenomena, 

 which may be described as the dragging or propulsion of 



