78 Intelligence and Miscellaneous Articles, 



departure and return, was 1206*5 metres. The temperature of the 

 water at the top of the conduit was 20°, and 13° at the bottom. 

 The temperature of the surrounding air was 18°. Under these con- 

 ditions the velocity of the propagation of the compression was found 

 to be 897*80 metres per second. 



The second and the third return shocks were too feeble to enable 

 us to deduce any accurate measure. 



Wertheim deduced, from the sound given by brass organ-pipes 

 dipping in water, 1173 metres per second as the velocity of sound 

 in water. This number is much less than 1435 metres per second, 

 found by MM. Colladon and Sturm in direct experiments made on 

 the Lake of Geneva. 



The value which I found is still further from the number observed 

 in an indefinite mass of water. Notwithstanding this divergence, 

 which I do not pretend to explain, I think it useful to give my re- 

 sults, which subsequent studies may confirm. 



I confine myself to calling the attention of physicists and geome- 

 ters to the influence which the elasticity and friction of the con- 

 taining sides may have on the propagation of a shock in the midst of 

 an almost incompressible fluid. Probably the difference between the 

 propagation of a shock in an indefinite medium and that which we 

 observed in a cast-iron cylinder is due to this circumstance. — Comptes 

 Rendus, March 14, 1870. 



EXPERIMENTAL RESEARCHES ON THE DURATION OF THE ELEC- 

 TRIC SPARK. BY MM. LUCAS AND CAZIN. 



The apparatus which we use to measure with accuracy the dura- 

 tions of electric sparks depends essentially on an application of the 

 vernier. 



A mica disk, 15 centims. in diameter, blackened on one face by 

 a photographic process, and divided near its edge into 180 equal 

 parts by means of transparent marks, is mounted on a horizontal 

 axis, which may be made to rotate with a velocity varying from 100 

 to 300 revolutions in a second. A crank and gear govern this rapid 

 motion. For one turn of the handle the mica disk makes 66^ turns. 



Another disk, of the same radius and centred on the same hori- 

 zontal axis, is fixed vertically, as near as possible to the moveable 

 disk. It consists of silvered glass, and has, towards the summit of 

 its vertical diameter, six transparent marks, which form a vernier, in 

 order to estimate the sixth of the interval between two consecutive 

 marks on the mica disk. 



The two disks are enclosed in a circular box of blackened copper. 

 The vernier forms the bottom of it, on the side of the source of light. 

 The mica disk turns in the interior. On the side of the observer 

 there is a metal plate for a cover ; a small aperture, provided with a 

 plate of glass, is arranged opposite to the vernier in order to admit of 

 observations. In this manner the moveable disk is preserved from 

 dust, protected against shocks, and sheltered from currents of air. 



The general appearance of this chronoscope, which has been very 



