190 ANNUAL OF SCIENTIFIC DISCOVERY. 



hands and legs, and their delineation in any thing like true proportion 

 and in good definition, cease to distract the mind. Each small head is 

 taken with the center of the lens, and is unexceptionable in definition ; 

 and as the full aperture of the lens may be used without hesitation, the 

 exposure is so rapid that there is no difficulty in obtaining good expres- 

 sions, an end which is further aided by the entire absence of all torture 

 in the way of arranging awkward limbs, a process so frequently fatal to 

 a pleasant or natural expression in the face. As to the question of 

 likeness and versimilitude, the interest of this style of picture must at 

 once commend itself to every one. 



We have not space now to enter into a detailed description of the 

 mechanical arrangement employed in getting the best result with the 

 least trouble. A very ingeniously-contrived dark slide has very simple 

 movements for obtaining the four portraits in their due positions, and of 

 the right size on the plate. When printed and mounted, the convexity 

 of each disc is produced by means of a steel punch and an arming press, 

 which is worked very quickly. The exquisite surface given by the face 

 of the die to the picture, fir exceeds that produced by rolling. 



The general effect is that of four cameos or enamels dropped on the 

 card. 



EFFECT OF ATMOSPHERIC PRESSURE IN GUNNERY. 



The French artillerists in Mexico have recently found, to their sur- 

 prise, that the angle of elevation used in France for their guns, for 

 any given range, does not afford the calculated results ; and have as- 

 cei'tained that this is owin_^ to the diminished pressure of the atmos- 

 phere oa the Mexican plateau. It follows that cannon may serve as a 

 kind of barometer for measuring altitudes. Les Mondes. 



INTERESTING BALLOON EXPERIMENT, 



A small balloon constructed of goldbeater's skin, scarcely two feet 

 in diameter, ascended from Highgate, England, on the 30th June, at 

 7 45 P. M., the wind blowing moderately from the X. W. A small 

 tube fitted to the neck allowed the gas to escape as it expanded, and 

 a paper car, filled with sand, which fell slowly through a small aper- 

 ture in the bottom was attached to the balloon, in order to compen- 

 sate to a certain extent for the gradual loss of gas. At 8 30 A. M., 

 the following morning it descended near Bamberg in Bavaria. The 

 distance is about 500 miles in a direct line, and the time occupied, 

 allowing for the difference of longitude, as nearly as possible 12 hours. 



DOES THE MOON REVOLVE ON ITS AXIS ? 



The following reasons may be advanced as a conclusive proof that 

 our moon does not revolve on its axis. . 



If our moon revolves on its axis, then any number of moons going 

 around the earth in the same way, each must equally turn upon its 

 axis, and analogously if a succession of moons, performing each the 

 same motion as the single one now does, were so closely packed as to 

 form one continuous ring, like that of Saturn, does any astromoner 

 claim that all the parts, forming that ring, would have a distinct axial 

 revolution? If so, then each imaginable section of Saturn's rin^s 



c5 



must also revolve on its axis ! which is an impossibility. If the con- 

 nected serif s do not revolve on their axis, no one of them can, as the 



