398 



Intelligence and Miscellaneous Articles. 



The whole of the experiments which I have made during the 

 last two years have led me, as an application, to the construction 

 of a musical instrument of an entirely new quality of tone, ap- 

 proximating to the human voice. I have given it the name of 

 pyrophone. This instrument is composed of three key-boards, 

 which can be united like those of the organ. With the aid of very 

 simple mechanism, all the keys are connected with the feed-pipes 

 of the flames in the glass tubes. When one of the keys is pressed, 

 the flames separate and the sound is immediately produced; as 

 soon as the performer ceases to act on the key, the flames come 

 together and the sound ceases. — Comptes Mendus de VAcademie des 

 Sciences, March 17, 1873, p. 699. 



ON A NEW OPERATION BY WHICH THE VELOCITY OF PROJECTILES 

 CAN BE DETERMINED OPTICALLY. BY MARCEL DEPREZ, 



An important advantage in using artillery would be an exact 

 knowledge of the form of the trajectory of projectiles fired under 

 high angles, as well as their velocity at each point of the trajectory. 

 Unfortunately the methods hitherto applied to very flat trajec- 

 tories are totally inapplicable to firing under high angles. In 

 reflecting on the means for supplying this deficiency, I have been 

 led to devise a process which, applicable to many other questions 

 besides that dealt with in balistics, I think it will be useful to 

 make known. 



Suppose that on the ground-plan of the polygon two stations, 

 A and B, be chosen, at each of which is placed a telescope. The 

 optical axes of these telescopes must be in one and the same 

 vertical plane perpendicular to the vertical plane taken by the 

 axis of the piece ; and the stations A and B are to be situated at 

 nearly equal distances from the intersection of the two planes. 

 The projectile is to be furnished with si fusee shedding a bright 

 light (magnesium would doubtless be very suitable for the purpose). 

 This being admitted, we shall suppose that, the piece being pointed 

 at a constant angle and firing several times in succession with the 

 same charge and the same projectile, the resulting trajectories will 

 pass constantly within the field of the telescopes. Then it is evi- 

 dent that, knowing the angles a and j3 which the optic axes of the 

 latter make with the base A B at the moment when the two ob- 

 servers simultaneously perceive the projectile, as well as the length 

 of that base, we shall have all the elements necessary for deter- 

 mining the coordinates of the intersection of the trajectory and the 

 vertical plane passing through A B. This process, however, in 

 principle the same as that employed for bolides, would not give the 

 velocity of the projectile at the moment it passes before the ob- 

 servers. To determine this element I propose the following 

 means : — 



With each of the telescopes is coupled a parallel telescope, of the 

 -Mime power, furnished with a reticule the- wires of which subtend 



