104 Mr Meikle 07i a proposed Improvement 



as this experiment might be often repeated in the course of a 

 few minutes, ample opportunity would be afforded for deter- 

 mining the exact distance which should make the two setisations 

 perfectly harmonize. 



But instead of watching the motions of the hammer itself, a 

 more precise and conspicuous signal might easily be contrived ; 

 such as a long index, cojnpleting a revolution during each in- 

 terval between the strokes, and then passing or covering some 

 conspicuous mark or line. For experiments in the dark, a small 

 hole might be opened, and instantly shut by the clock-work, at 

 the very nick of time to allow a lamp placed behind a screen 

 sending a momentary ray to the observer. 



This brief outline, I hope, will make it evident, that such 

 machines, in proper hands, would tend in a great measure to 

 obviate the uncertainty inseparable from hurriedly measuring 

 the short interval of time v/hich elapses during the motion of 

 the sound of bells over small distances. For, if the visible sig- 

 nal be observed exactly to agree with the sound, we are sure of 

 the true elapsed time, from the rate of the clock, without flus- 

 tering ourselves to measure it at the moment. The observer, 

 in this mode of operating, would merely be required to walk a 

 very little backward and forward till he found himself at the 

 exact distance. But, as neither eyes nor ears are in all per- 

 sons equally acute, several observers might be employed at 

 each station ; and if they did not exactly agree about the dis- 

 tance, this might lead to a more minute investigation of the cir- 

 cumstances. 



For the better obviating the eflPects of wind, a clock would be 

 required at each end of the base over which the sound was to 

 pass. They need only be pieces of strong machinery, without 

 any compensation to the pendulums ; and yet from them the 

 minute interval of time could be obtained, to a degree of exact- 

 ness to which the nicest chronometer, when used as formerly, 

 can have no pretensions : For the method now proposed pos- 

 sesses the same sort of advantages over the former method, that 

 Hadley's quadrant does in measuring angles at sea over the old 

 instruments. 



The theory of sound is besides very imperfect, otherwise it 

 would not leave us so much in the dark regarding the sovereign 



