218 



REPORT — 1861. 



Nor is it due to relative differences of different experiments in the lengths 

 of range, in the quartz rock and in the slate respectively, as might be 

 imagined ; for the experiments Nos. 2, 5, and 6 had wave-paths of about 

 1400 feet in quartz only, and embrace the lowest and the highest velocities, 

 while Nos. 1, 3, and 4 had about double this range or wave-path in quartz, 

 with velocities not widely different from each other, or from No. 2. 



There are four corrections altogether applicable to the uncorrected transit- 

 rates, col. 8, Table I., as already referred to, viz. — 



1st. That for the liquid wave in the seismoscope, which, as a delay in 



time, is, when converted into distance, always + . This correction has 



been already applied in cols. 9 and 10, Table I. 



2ndly. That for the time of hang-fire of each explosion in the rock, the 



constant in time for which has been given, =0"'056. 

 It appeared, however, uncertain whether this should be converted into di- 

 stance, as probably nearly constant for every experiment, or in what way 

 it might be variable, in relation to the weight of powder, and other circum- 

 stances of each. The result disclosed in Table II., however, appears to 

 indicate that the conversion into distance should be proportionate to the 

 respective gross or uncorrected transit-rates, assuming, as we may now do, 

 that these are functions of the originating impulses and resistances together, 

 in each instance. This may not be absolutely true, but is the nearest ap- 

 proximation we can make. This correction in distance is also always + . 

 3rdly. The loss of time at making contact, — whether galvanically, in 



which we ascertained the constant in time to be =0 "•0143, when converted 



into distance always -f-j or by the hand (of the firing party), when we found 



it was in time =0"*013, which in distance might be either + or — . 

 The probability being so much in favour of the latter being positive, I have 

 ventured to apply it as always so, which also renders all the experiments 

 more truly comparable. 



4thly. The personal equations of the observer and time of transit of the 



galvanic current, both of which may be neglected. 



Applying these several corrections, we obtain the following Table and final 

 numerical results : — 



Table III. — ^Wave-transit Experiments. Corrected Results. 



The limits of error in these results would seem to be, that the 2nd correc- 

 tion may amount to 15'5 feet per second in excess, and the error from all 

 other instrumental or observational sources may be estimated probably at 

 not more than 10 feet per second, so that the results may be deemed true to 

 within 25\ feet per second + or — . 



