310 Intelligence and Miscellaneous Articles. 



very short focus, and with a suitable shutter devised by M. Duboscq. 

 The focussing is easily effected, either by moving the object-glass, 

 or, better, by moving the manometric flames. 



The motion of the flames to be photographed is so rapid that we 

 should have recourse to the most sensitive plates. Those of Monck- 

 hoven have given very good results ; I prefer, however, the very 

 sensitive plates prepared with silver iodide by Frank's formula. 



But whatever be the plates used, the negatives will always be 

 too weak if we do not take the precaution of using a lens 

 of short-focus, and of making the flames as bright as possible. 

 This is attained if we carbonize the gas by passing it through 

 pumicestone impregnated with benzole, and burning it in pure 

 oxygen. By suitably regulating the supply of gas and oxygen, we 

 obtain a flame of great lustre. 



The plates are developed by the ordinary photographic methods ; 

 they have then two rows of parallel dentations, one of which cor- 

 responds to the vibrations of the chronographic flame, and the 

 other to the vibrations of the flame worked by the sound whose 

 height is to be measured. 



The comparison of the two flames is then an easy matter. It 

 may be made in two ways; either by the measurement of the 

 number of vibrations and fractions of vibrations comprised within 

 equal lengths, or by the determination of the space occupied by 

 known whole numbers of vibrations. 



If the height of the flame has been suitably adjusted, so as to 

 give images of 1*5 to 2 millim., these measurements are made with 

 great facility and remarkable precision. 



This method, devised for the purpose of lengthened researches 

 on the vowel sounds, has been verified with great care for the 

 sounds corresponding to the scales Ut 15 Ut 2 , TJt 3 , aud Ut 4 by the 

 aid of the chronograph Ut 3 , of sliding diapasons, and of open pipes 

 constructed by M. Konig with his usual care. 



The following table shows the certainty and accuracy of the 

 method, since the distances between the heights found and the 

 heights indicated do not exceed a double vibration : — 



Number of m te. 

 plates. 



99 Ee 2 



102 Mi 4 



103 Ut a 



100 trt 4 



101 Sol 3 



Heights 





—N 



Measured. 



Indicated 



287-88 



288 



1280-00 



1280 



256-20 



256 



1022-50 



1024 



767-10 



768 



To measure very high or very low sounds, it is good to have 

 recourse to two chronographic diapasons, one giving 100 vibrations 

 per second, and the other about 2000. In this case in fact, where 

 the difference of height between the two sounds is too considerable, 



