Velocity of Transmission of Disturbances through Sea-water. 523 

 or, substituting the values already found for sea- water, 

 Velocity = 



/ 1 



V D(481X 10-7-340 x 10- 9 t + 3x 1Q-»S*) (273 + Q (-000221)8 , 

 1014412 42xl0 6 x-962 



As stated before, the velocities thus calculated are given in column 12 

 of the general table. The calculation is laborious. 



Explanation of the General Table. 



The Table explains itself except with regard to the observations on 

 July 11, and the three first on August 10. In these cases a mean of 

 three intervals was taken by taking a mean of two shots in the 

 direction left to right, and then a mean between that mean and the 

 interval from right to left. It is to be remarked that in the case of 

 the pair of shots on September 13, which gave the mean interval 

 0*1277, the mark on the smoked plate determining the single interval 

 0*1210 was extremely faint. A photograph of this plate is shown 

 (p. 524), the single radial line showing the slight break in the line 

 traced by the scriber. 



On the lower part of the General Table are given the observations 

 from which a mean interval could not be obtained, together with the 

 first observations on April 25 and May 7, and another pair of ob- 

 servations on July 5. These observations were rejected on account 

 of the gauge having been water-logged ; besides this they should be 

 regarded with suspicion, since they would give results whose 

 departure from the final mean wo a Id be greater than the " maximum 

 error" found in accordance with the theory of adjustment of 

 observations. 



It may be added that as a general result of our experience we found 

 that (possibly owing to some interference effects) the distant gauge 

 was often more violently affected after its first indication. Now 

 when the gauges were water-logged they became deficient in 

 sensitiveness, and consequently in the observations referred to the 

 probability is that the mark observed corresponded to the second, not 

 the first shock. This conclusion is strengthened by a reference to 

 the photograph of the plate of September 13. 



Paet III. — Reduction and Discussion of Results. 



The experiments are divided into four classes, according to the 

 nature and quantity of the explosive used. In Class A the explosive 

 was a 9-0Zc disk of guncotton, in Class B 10 oz. of dynamite, in 

 Class C 18 oz. of guncotton, and in Class D, 4 lb. of guncotton. In 



