338 THE THUNDERSTORM OF OCTOBER 26, 1888. 



requirements of the ordinary arts, in which there are many processes 

 which require this extreme accuracy of measurement if it can be 

 applied automatically at a moderate cost, and this can readily be 

 done. I may state however that this application of the method 

 of electric contacts confirms the view founded upon some early 

 experiments, which I expressed two months since, viz., that it 

 will be possible in this way to record with certainty changes in 

 the direction of the vertical of -^ of a second of arc, and to plot 

 these out on a cylinder shewing the amount of such changes, and 

 their direction, as a check upon the transit instrument, and it may 

 be interesting to add that a change of --fa of a second of arc is one 

 that even the best modern transit instrument is hardly capable of 

 shewing satisfactorily. 



THE THUNDERSTORM OF 26th OCTOBER, 1888. 

 By H. C. Russell, B.A., F.R.S., &c. 



[Bead before the Royal Society of N.S.W., November 7, 1888.~\ 



There are one or two points about this storm that seem to me to 

 be worth recording. On the morning of the 26th there was a 

 remarkably sudden rise in the barometer, but the barometer 

 gradually fell during the day and seemed to be fairly steady, with 

 a tendency to fall. In the afternoon it was evident that a 

 thunderstorm was approaching. At 6-45 p.m. the barometer 

 turned to rise slowly and the storm began soon after with very 

 very frequent flashes of brilliant lightning and a sudden change 

 of wind to N. thence round by West to S and S.E., the change, 

 the latter part of it from W.S. W. to S.E. occupying half an hour, 

 during which time the barometer at first rose rapidly for ten minutes 

 to the extent of 0*073 then fell for fifteen minutes at the rate of 

 O'l inch per hour, and then very rapidly, so that at the end of 

 half an hour from the time the fall began it had fallen # 15 inch, 

 which is at the rate of 30 inch per hour ; the latter part of this 

 fall was almost as rapid as the phenomenal one on the 21st of 

 September last, which you may remember was 0-044 in one minute ; 

 in this case it was 0-040 in one minute. So rapid was this fall 

 altogether, that the Redier barograph only recorded a change 0*10 

 not being able to follow such a rapid change, but the new barograph 



