Intelligence and Miscellaneous Articles. 157 



The determination of the duration of the combustion of a fuse is 

 rather uncertain if the observer himself wishes to note on any chro- 

 no metric apparatus the moment at which the fuse kindles, and that 

 at which it finishes. There is great risk of the introduction of per- 

 sonal errors, which are different in different cases. In order to avoid 

 these errors, I measured the duration of the combustion by means 

 of an electric register. The fuse was lit by a pistol, in which the 

 fall of the lock broke the current. The end of the combustion ex- 

 ploded a small quantity of powder, which, by letting a metallic rod 

 fall, again completed the circuit. The duration of the phenomenon 

 was thus indicated on the register by the interval between two con- 

 tinuous marks ; this interval is easily transformed into time by a 

 known process, which it is needless to develope here. Preliminary 

 experiments were made in order to ascertain the degree of exactitude 

 of which the method and the apparatus were susceptible. These 

 experiments show that the possible error did not exceed -j^-th of a 

 second. 



Two groups of fuses were submitted to experiment under five 

 different pressures, varying between 730 millimetres and 538 milli- 

 metres. The fuses were not *so identical as to burn for exactly 

 the same time under the same pressure. To know the influence of 

 the density of the external air, it was necessary to burn a certain 

 number of fuses in the same place, and then to take the mean : a 

 comparison of the means ought to show the influence of the pressure. 

 In order to neutralize as much as possible the inconvenience arising 

 from the difference in the fuses, the means of eight to ten experi- 

 ments were taken at each station. Altogether 68 fuses were 

 burned in the five stations. The crest of the Chenallettes, which 

 commands the Convent of St. Bernard at 9700 feet above the sea- 

 level, is the highest station of the series. With some difficulty the 

 instruments were moved to and fixed at this elevated position. 



The fuses of the first group unfortunately presented considerable 

 individual differences. Those of the second group were much more 

 regular. The following is an abstract of the means : — 



Station. Height. 



metres. 



Ouchy 380 



Gonize 920 



St. Pierre 1640 



St. Bernard . . 2478 



metres. 



Ouchy 380 



St. Pierre 1640 



Chenallettes . . 2890 



First Group. 







Pressure. 



Mean 



Mean 





Duration. 



Difference 



millims. 



s. 



s. 



728 



9-96 



0-52 



685 



10-11 



0-54 



628 



10-52 



0-50 



568 



11-20 



0-55 



Second Group. 







millims. 



s. 



s. 



731 



9-15 



0-23 



628 



10-12 



0-29 



538 



11-09 



0-26 



