138 : The Flood Rock Explosion, [ February, 
scope in connection with a horizontal plane of mercury, the sun 
thermometer, the thermometer, the ł ter, the pluviometer, etc. 
The shock did not create as much noise as an ordinary field 
piece. 
The shock was felt by the feet and indicated by the seismo- 
scope one-half a second before the result was visible to the eye. 
The seismoscope, which is supposed to record the beginning 
of the shock simply, traced an unintelligible record on the side- 
real time cylinder at the Columbia College observatory. 
Observers who watched horizontal planes of mercury through 
telescopes naturally report different results. Professor William 
Halleck, at Yonkers, N. Y., ten miles from the explosion, records 
that the vibration of the mercury increased after the first fifteen 
seconds up to forty seconds, then diminished for ten seconds, 
ceasing entirely after fifty seconds, Professor J. K. Rees, at the 
Columbia College observatory, two miles away, and Professor 
Young, at Princeton, record that the duration of vibration of the 
mercury was thirty seconds. Professor W. A. Rogers, at Har- 
vard College observatory, 197 miles away, records that the vibra- 
tions lasted there two minutes and forty-six seconds. This would 
show that the earth wave divided constantly as it traveled out- 
rd. 
All of the instruments of the Central Park observatory left a 
record very much to the amazement of Professor Daniel Draper 
and other meteorologists. Why, for instance, should such a dis- 
turbance in any way affect the sun thermometer and rain gauge? 
The former recorded 121° in the sun, when suddenly the pen, 
which was tracing its record on paper, made a straight mark 
eight degrees long at right angles with the regular tracing and 
with four degrees on each side of it. This would naturally show 
a decrease or increase in the sun’s temperature, whereas it was 
really an interruption of the sun’s record by an abnormal cause. 
Professor Draper thinks that this record must be of great value 
to seismologists. I think it shows that the record of a sun 
thermometer, as indicated by a tracing on paper, cannot be relied 
upon, since any jar is liable to affect it. The pluviometer, or rain 
gauge, also gave an uncalled-for record of one-eighth of an inch. 
While these records may be of value to some one who can utilize 
them, to my mind they only demonstrate the fallacy of placing 
any value on the record of these instruments as traced on paper. 
