A striking result which was obtained by Mallet in his experiments at Holyhead was that the transit velocity increases with an increase in the intensity of the initial shock. Thus with a charge of 12,000 pounds of powder the transit rate was 1,373 feet per second, whilst with 2,100 pounds the transit rate was 1,099 feet per second. In these experiments tremors were observed as preceding and following the main shock. _Abbot’s Results._—The important results obtained by General Abbot are contained in the following table:— A. No. of Observation B. Distance to Station in miles C. Type of Seismometer D. Velocity in feet per second +--+----------------+--------------------------+--------+---+-------+ | A| Date | Cause of Shock | B | C | D | +--+----------------+--------------------------+--------+---+-------+ | 1| Aug. 18, 1876 | 200 lbs. of dynamite | 5 ± | B | 5,280 | | 2| Sept. 24, 1876 | Hallet’s Point Explosion | 5·134 | A | 3,873 | | 3| „ | „ „ „ | 8·330 | B | 8,300 | | 4| „ | „ „ „ | 9·333 | A | 4,521 | | 5| „ | „ „ „ | 12·769 | B | 5,309 | | 6| Oct. 10, 1876 | 70 lbs. dynamite | 1·360 | A | 1,240 | | 7| Sept. 6, 1877 | 400 „ „ | 1·169 | A | 3,428 | | 8| „ | „ „ „ | 1·169 | B | 8,814 | | 9| Sept. 12, 1877 | 200 „ „ | 1·340 | A | 6,730 | |10| „ | „ „ „ | 1·340 | B | 8,730 | |11| „ | 70 „ „ | 1·340 | A | 5,559 | |12| „ | „ „ „ | 1·340 | B | 8,415 | +--+----------------+--------------------------+--------+---+-------+ A seismometer of type A means that the telescope used in observing the tremor produced on the surface of a vessel of mercury by the passage of the shock had a magnification of 6, whilst a telescope of the type B had a magnification of 12. The mean velocity given by six observations with type A is 4,225 feet per second, while that given by the same number with type B is 7,475 feet per second. [Illustration: FIG. 13.] If we assume that the first tremor observed in the mercury is to determine the true rate of transmission, General Abbot tells us that we must reject all observations made with type A, inasmuch as they do not reveal the velocity of the leading tremor. However, he also tells us that a still higher power above 12 might have detected still earlier tremors. When gunpowder was the explosive, the observers noted that the disturbance observed in the mercury took a much longer time to reach a maximum than it did when dynamite was employed.