Transactions of section a. 33o 



The study of a few such cases shows how well the ground is covered by the few 

 figures given, except perhaps near 1\, 8£, and 9£ years. To strengthen the investiga- 

 tion near these periods it is easy to calculate the values of a 2 + b' 2 from the numbers 

 for 15, 17, and 19 years respectively, using sin 2 9 and cos 2 9 instead of sin 9 and cof 9. 



The results are as follows and show that nothing has been missed : — 



The study of the periodogram for periods shorter than seven years is' more 

 profitably undertaken by forming numbers afresh for (say) every four months, so 

 that in seven years there would be 21 observations. Beginning with 20 of these we 

 can work down to seven, representing a period of 28 months ; and then we could 

 begin again with single months. The present note practically clears away the 

 long periods which could be detected from available material ; for it is doubtful 

 whether existing observations could satisfactorily confirm any longer period than 

 twenty years, from two hundred years of record only. 



4. Horizontal Pendulum Movements in relation to certain Phenomena. 

 By P. Napier Denison, F.R.Met.Soc. 



The object of this paper is to present in as brief and graphic a manner as 

 possible the results of observations carried on upon the Pacific coast for a series 

 of years. 



In the autumn of 1898 a Milne horizontal pendulum was installed at 

 Victoria, B.C., and is one of many throughout the world whose records furnish 

 valuable data for the Seismologica] Committee. Apart from the shorter period 

 vibrations as quakes, tremors, &c, so graphically shown upon these traces, the 

 author became deeply interested in observing certain wanderings of the pen- 

 dulum; some lasting for days and sufficient to necessitate adjusting the levelling 

 screw to keep the free end of the pendulum upon the centre of the paper. 

 Thinking these movements might be due to changes of atmospheric pressure, 

 the author began keeping a continuous record of these changes from January 



1899, by measuring the exact position of the boom each day at noon, and 

 allowing for certain levelling adjustments necessary from time to time. 



A daily curve from these observations was plotted for the years 1899 and 



1900, and when studied with the Synoptic Weather Charts of the Pacific slope 

 for the same period, it was shown that the pendulum which is placed in the 

 meridian would swing towards the eastward when the barometer was highest 

 over the Pacific slope, and in the opposite direction when the barometer was 

 low in this vicinity. These movements often commenced some hours before 

 the local barometer indicated an approaching change. These observations 

 formed the material for a paper read in 1901 before the Royal Meteorological 

 Society, 1 and in the autumn of that year further data upon the same subject 

 was personally presented at the British Association meeting held at Glasgow. 



Acting upon the advice of Sir George Darwin to continue the E.-W. pen- 

 dulum observations, and to establish a N.-S. instrument, I have succeeded in 

 keeping a continuous record of the former to the present time, and in 

 January 1907 personally constructed another instrument. This one is mounted 

 in the basement of the Post Office upon solid rock and is about five hundred feet 

 distant from the E.W. pendulum, and is set to swing N.S. 



In 1908 daily curves for both pendulums for the year 1907 were plo':ted. 

 These when studied with the weather charts of this coast showed that, both 

 pendulums had a general tendency to move in the direction where the air 



2 ' The Seismograph as a Sensitive Barometer.' 



