TRANSACTIONS OF THE SECTIONS. 39 



On the Diurnal Variations of the Barometer and Wind in Mauritius. 

 By C. Meldkum, F.R.S. 



On the Meteorology of Plymouth. By John Merrifield, F.B.A.S. 



The deductions drawn in the paper are from observations taken daily at 8 a.m. 

 for the past twelve years, viz. from 18G5 to 1876, both inclusive. 



I. Atmospheric pressure — The average is 29945 in. ; the months of greatest pres- 

 sure are June, 30-059, and July, 29 - 996 ; the months of least pressure are January and 

 October, both being 29'868 ; these months correspond with a great and small rainfall. 

 February and April to August have a mean pressure below the average, whilst the 

 other six months have a pressure above it. The mean monthly range is l - 074in., 

 those of greatest range being January, February, November, and December, and 

 those of least range are July and August. The greatest ranges correspond to 

 the months of least pressure and vice versd. 



II. Temperature. — The coldest month is January, whose average is 42°-82 F., 

 which is half a degree lower than December ; but the nights of March are colder 

 than those of February. The hottest month is July, whose average is 63 0, 56 P., 

 which is about 1° F. higher than August. The lowest maximum I have recorded is 

 28° F. on 22nd December 1870, and the highest minimum 67° F. on 27th August 

 1869. The maximum temperature during the twelve years is 93° F. on 27th 

 June 1866. The minimum is 14° F. on 27th December 1869. The mean 

 daily range is 20° - 74 F. ; the greatest daily range was on 27th April 1865, 

 when it was 44° F., with a maximum of 86° F. The least range was on 22nd 

 December 1870, when it was 2° F., with a maximum of 28° F. The averages, 

 according to the author's returns, agree with those published by the British 

 Association from 1833-7, within one tenth of a degree. 



III. Wet and Dry Bulbs. — The greatest difference between the bulbs is in June, 

 3°-79 F., and July, 3°-56 F. The least difference is in December, -89, and January, 

 •94. The relative humidity for May, June, and July is 79°-77 and 79° respectively, 

 whilst that for October is 93°. The greatest difference recorded by the author 

 between the bulbs is 15° on June 22nd, 1865, when the dry bulb was 78° and the 

 relative humidity was 41° ; but this occurred after several days of continuous 

 easterly winds. 



IV. Rainfall. — January has the greatest rainfall, as well as the greatest number 

 of rainy days, viz. 4*852 inches in 21*15 days. June has the least of each, viz. 

 1-375 inch in 9J days. September stands fifth in order of rainy days, but is 

 second in order of rainfall ; hence, if we neglect thunder-showers, our heaviest rains 

 must occur in that month. We have nearly twice as much rainfall in the six 

 months from September to February as during the remaining six months ; whilst 

 the number of rainy days is almost as 3 is to 2. We sometimes have heavy showers, 

 as on 29th July, 1871, when in less than half an hour three-quarters of an inch of 

 rain was registered; and sometimes, though rarely, suffer from want of rain, as, for 

 example, from 18th March to 2nd July, 1870, when, if we omit a thunder-shower 

 on 12th May, only l - 3 inches of rain fell in 106 clays ; but on the average we have 

 rain amounting to more than '1 inch every day. 



V. Winds. — We get 195 westerly to 144 easterly winds in the year, or the days 

 on which westerly winds and calms prevail are 20 per cent, more than those on 

 which easterly ones blow. The months of July and August have the greatest 

 number of westerly winds ; March, April, and May have the greatest number of 

 easterly winds. Winds of greatest violence blew in November, December, and 

 January. 



We get 20-49 per cent, of winds from N. by E. to E. 

 19-21 „ „ E. by S. to S. 



20-85 „ „ S.bvW.toW. 



23-70 „ „ W.byN. to N. 



and 6'75 „ calms. 



VI. Thunder-storms. — Judging from newspaper reports, thunder-storms are rarer 



