354 



NA TURE 



\\ I nous? 7, 1884 



but also those for which none were sent out, thej affi 

 index to the storms which have been felt on the 



Only such storms have been selected as have been really 

 severe, such as have attained force 9 of the Beaufort scale at 

 more than two stations, with a velocity exceeding 50 miles an 

 hour recorded by an anemograph fa- more than a single hour. I 

 have also not discriminated between the directions from which 

 the strongest winds were felt. 



The results of these records show that gales are of no greater 

 frequency at the equinoxes than at any other time. 



The diagrams show that the storms are all but exclusively 

 confined to the winter half-year, if we take that to include part 

 of the autumn and spring. 



The diagrams show that there is no strongly-marked maxi- 

 mum at either equinox, but they do exhibit indications of period- 

 icity which are very interesting. 



', > the summer alone, as not worth notice, the frequency 

 nine and eight in the periods preceding the autumn 

 equinox to ten at that epoch. The curve then rises rapidly, the 

 value doubling itsell and trebling itself in the two succeeding 

 intervals. We then find a falling off at the time of the Martin- 

 mas iummer in the first half of November, and a second maxi- 

 mum in the end of that month — the period indicated by Sir 

 Tohn Herschel long ago, in an article in Good Words for January 

 1864, as that succeeding what he called "The Great November 

 ■ which does not receive as much attention 

 now as formerly. The first part of December is comparatively 

 quiet, but after that the frequency rises to its absolute maximum 

 at the latter half of January, from which period the curve de- 

 scends gradually, with one decided check in February, to the 

 same value which it had in August, and which it attains at the 

 end of April. The check in February reminds us of the well- 

 known tradition of the " halcyon " days at the end of winter. 

 The frequency at the spring equinoctial period is nearly 

 double wl the corresponding interval at the 



autumn equinox, being 19 as compared with 10. In one 

 particular, however, the phenomena agree — the equinoxes are 

 periods of sudden change in storm frequency. In the autumn 

 this rises from 10 to 20 as soon as the equinox is passed ; 

 in the spring it falls from 27 to 19 as the equinox arrives. 

 Accordingly, persons who wait till the equinox is passed in 

 autumn improve their chances of falling in with a storm, for the 

 diagram shows no signs of a lull once a heavy storm has oc- 

 curred. In the spring it would apparently be wise to wait till 

 April was well advanced, if you wished to get calm weather in 

 the Bay of Biscay. 



If we now look to see what evidence of recurrence of storms 

 for particular short periods is discoverable in our data, we find 

 that the day most frequently so distinguished is January 1, on 

 which a storm was recorded six times in the fourteen years. 

 This is very remarkable, as December 31 only shows one, and 

 January 2 only two storms. Five days — November 10 and 20, 

 January iS and 10, ami February 26 — show five each, and no 

 less than sixteen days show four. The stormiest two-day inter- 

 val is that of January iS and 19, which, as just explained, ex- 

 hibits five storms each. The most disturbed three-day period is 

 that of January 24 to 26, where we find four storms on each 

 day. The date of the Battle of Trafalgar, October 21, is marked 

 by two fours, on the 21st and 22nd, but the end of October is not 

 so distui I of January. 



The diagram also shows that almost every month in the year 

 is occasionally nearly free from storms. October, November, 

 December, and January have only one apiece, but in different 

 years. March is the only month which has at least two storms, 

 thus justifying its epithet, " March many-weathers." 



Mr. Scott also read a paper on Cumulative Temperature, of 

 which the following are the leading points : — 



On the walls of the Meteorological Annexe will be found a 

 series of diagrams, exhibiting from various districts in the United 

 Kingdom, in a graphical form, the March of Temperature, 

 Rainfall, and Bright Sunshine, from the beginning of the pre- 

 sent year, and also for the entire year 1SS1, which is reproduced 

 for purposes of comparison. 



The object of these curves is to show clearly some of the most 

 important factors in the growth of crops. 



It is proved, almost beyond a doubt, that each plant, say each 

 individual cereal, requires a definite amount of heat to bring it 

 to maturity. Thus, maize requires more than wheat, and wheat 

 again more than barley or oats. 



Now various investigators, and notably Boussingault and Prof. 



Alphonse de Candolle, of Geneva, have devoted much attention 

 1" this subject, and the latter writer, in his "Geographic 

 Botanique," has come to the conclusion that a certain total 

 amount of temperature above a definite base line is necessary 

 for plant growth, and that this amount, or, as he calls it. this 

 " sum of temperature," varies for each crop. 



lie found that plants, as a role, did not begin to give indica- 

 tions of active vegetation until the temperature rose above 6' C. 

 This temperature, 6" C, or, in round numbers, 42 F., that is 

 ten degrees above the freezing point, is taken as the base for all 

 the diagrams. Although Prof, de Candolle propounded his views 

 some years ago, as recently as the year 1874, at the Agricultural 

 Conference a: Vienna, meteorologists were quite at sea a 

 attire were to be calculated. 



The credit of solving this problem belongs to Lieut. 



trachey, the Chairman of the Meteorological Council. 

 In the first : | oses to adopt a certain unit of 



ture to supply a standard for calculation, the unit being 0n< 

 degree continued for the unit of time, either one hour or 

 as the crse may be. Such a unit may be conveniently called an 

 hour degree, or day degree. The unit of time 'adopted for the 

 calculations to which I am about to refer is a day, and the unit 

 of what may be termed the effective temperature is therefore a 

 day degree. A day degree therefore signifies 1 ' . ■ 

 defect of temperature above or below 42" F. continued for 

 twenty-four hours, or any other number of degree-, for an 

 inversely proportional number of hours. 



Now the first idea I want you to take in about th 

 degrees is that when we speak generally of the mean or average 

 temperature for a day, or month, or year, we imply that the 

 resulting temperature is the same as would be observed if the 

 thermometer indicated this mean temperature throughout the 

 entire period for which the mean is taken. Thus, if we wen 

 dealing with daily means, an average daily temperature of 62' F., 

 which is an ordinary temperature for a warm sumrm 

 would mean twenty day degrees of temperature for that day, 

 starting from the assumed base line of 42 J F., which has already 

 been mentioned. 



The first step therefore towards determining this effective 

 temperature in day degrees resolves itself into determining as 

 speedily and simply as possible the average temperature for the 

 period under consideration. 



We have, fortunately, to our hands, a very simple mode "t 

 arriving at the mean temperature with accuracy sufficient for our 

 purposes. Almost all observers record the maximum and 

 mininum temperatures once in the twenty-four hours. It is 

 found that the half sum of these readings, the mean 

 them, is nearly but not exactly the average for the day. It 

 must, of course, be understood that the instruments must be 

 read regularly ami at the same hour every day. 



The next points which require attention are : whether the 

 maximum and minimum are both above 42', which occurs in 

 summer, or both below that point, which occurs in winter ; or, 

 finally, whether one is above, and the other below. In the first 

 case all the accumulated temperature is to the good ; it is all on 

 the positive side. In the second ease it is all on the negative 

 side. The third case is the only one which presents difficulty, 

 for when the extreme temperatures are on either side of the line 

 of 42 , one portion of the effective temperature for the day is 

 po-itive, and the other negative. 



Now, General Strachey carried out a long series of cal 

 based on the observed hourly temperatures at Kew Ol 

 and at other stations in the United Kingdom, in order to ascer- 

 tain the magnitude of the co-efficient by which the difference 

 between either of these extreme temperatures and the base tem- 

 perature (42° F. ) should be multiplied in order to obtain the 

 values of the temperatures in excess or defect of 42° F. expressed 

 in day-degref ind he found that this, for a weekly period, 

 was o .4. 



Accordingly we get the following rules : — 



If the mean of the day is above 42° F., we multiply the 

 difference between the minimum and 42' F. by 0'4 (four-tenths), 

 and call this the negative effective temperature. 



To find the positive effective temperature we subtract from 

 the difference between the mean for the day and 42°, the negative 

 effective temperature just determined. 



If the mean of the day is below 42° F. the proceeding is 

 similar ; but we first ascertain the positive effective temperature, 

 and subtract that from the difference between 42 1 . 

 mean, thus obtaining the negative effective temperature. 



