August 10, 1 882 J 



NA TURE 



539 



towards saturation in summer, the sky at the same time 

 becomes more completely cleared of clouds than in 

 winter. Thus the mean cloudiness in winter indicates 

 that four-tenths of the sky is covered, but in summer 

 there is only one- tenth. This increased relative humidity, 

 occurring simultaneously with increased clearness of sky, 

 is an important feature of the climate of Alexandria, being 

 productive of a heat in the direct rays of the sun much 

 less intense than the clearness of the sky and the latitude 

 might lead us to expect. 



The mean annual temperature is 68°7, the minimum 

 being 57°'6 in January, and the maximum 7S c- 9 in August. 

 The coldest January, 54" o, occurred in 1SS0, and the 

 warmest, 62 c ' 1, in the following year, there being thus 8 ,- i 

 of a difference. No such difference occurred in the 

 summer months. Thus the coolest August was 77°7 in 

 1876, and the hottest, 8o° - 2 in 18S0, the difference being 

 only 25. At Cairo the differences of temperature are 

 much greater. The daily range is considerably greater 

 than that of Alexandria ; the mean temperature of January 

 is 54" ' 1 , and of August 84°"5, and as regards variation of 

 the monthly temperatures from year to year, the mean of 

 January was 5o"o in 1880, but 59°'2 in 1S81 ; and the 

 mean of August was So c '6 in 1876, but 9o "7 in 1S77, the 

 daily range for the two seasons being thus <f'i and 10 1. 



At Alexandria the mean annual rainfall is 8'i2 inches, 

 falling on 44 days. The largest annual fall was 1075 

 inches in 1876, and the leaet 342 inches in 1879. The 

 following are the means in inches for the months: — 

 January I '95, February 1 46, March 072, April 015, May 

 and September 002 each, June, July, and August nil, 

 October 0-58, November 1*52, and December 170. Heavy 

 rainfalls are of occasional occurrence. During these seven 

 and a half years the fall for one day exceeded an inch on 

 13 occasions. The largest of these falls 300 inches, 

 occurred on October 7, 1876. Hail has been recorded 

 on nine separate days in all, and thunder and lightning 

 on eight days. 



The following peculiarity in the annual march of the 

 temperature is noteworthy. The mean temperature of 

 June is 7S° - o, July 77 = 5, August 78°'9, September 77°7> 

 and October 74°'4, from which it is seen that September 

 is warmer than July, and October nearly as warm as 

 June. This peculiarity is still more striking if we look 

 exclusively at the daily maximum temperatures which are 

 so important an element of climate. To show this, we 

 subjoin the means and extremes of the daily maxima; 

 week by week, from July 1 to October 27 : — 



Thus, then, we see that the highest temperatures during 

 the year have taken place in the end of September and 

 the first half of October, and that absolutely the highest 

 temperature yet recorded, I03° - l, was on October 11, 



1877 ; and that while the highest weekly mean occurred 

 in the latter half of August, a secondary maximum, nearly 

 as high, occurred in the beginning of October. It will 

 be also observed that up to the close of October, the 

 temperature is still nearly as high as in the beginning of 

 July, but after this date temperature rapidly declines. 

 That this is no chance result peculiar to the years of ob- 

 servation is shown by the recurrence of this feature of 

 the climate year by year, as well as by the temperature of 

 Jerusalem and other places in the East. 



Practically, from May to September inclusive, no rain 

 falls. The precise date of the commencement of rain 

 greatly differs in different years. The following are the 

 dates for each of the seven years, marking the earliest 

 day on which at least one-tenth of an inch of rain fell, 

 which may be considered as marking roughly the ter- 

 mination of the dry season at Alexandria : 01S inch on 

 November 4, 1875 ; 300 inches on October 7, 1S76 ; o"22 

 inch on October 16, 1877 ; 0-93 inch on November 29, 



1878 ; 027 inch on December 20, 1879 ; 015 inch on 

 September 27, 1880 ; from which date the rainfall was all 

 but ;//'/, till 0-14 inch fell on November 27, and 0-32 inch 

 on November 15, 1SS1 . Leaving out of view the small 

 sporadic fall in September, 1880, the earliest date for the 

 termination of the summer drought was October 7, and 

 the latest December 20, the mean date of the seven years 

 being November 12. 



On advancing from the Mediterranean sea-board into 

 the interior, the climate rapidly changes ; the rainfall 

 becomes less and less, and then practically ceises ; the 

 air becomes drier, and the sky clearer ; the sun's heat 

 stronger, the nights cooler, and the daily range of tem- 

 perature greater. At Cairo the rainfall is quite insig- 

 nificant in amount, but occasionally pretty heavy falls 

 occur. Thus on January to, 1S70, V02 inch fell, and on 

 May 3 of the same year 067 inch. From January to 

 May of the present year 116 inch has fallen, of which 

 o-8o inch fell during the six hours ending 7 p.m. of April 1. 

 The temperature rose at Cairo to H2"-6 on J'ine -, 1872 ; 

 to U3 : '2 on May 25, 1S73; and to Il6 0, 4 on May 20, 

 1869, the highest recorded at Alexandria being as stated 

 above, io3 = i. During September and October, the mean 

 temperature of the two places is nearly the same, with, 

 however, this essential difference, which must not be lost 

 sight of ; the days are much hotter and the nights much 

 colder at Cairo, where consequently greater precaution 

 must be taken against chills at night, these being the 

 fruitful source of diarrhoea, and other complaints which 

 often prove so disastrous during campaigns carried on 

 in such climates as that of Egypt. 



COLLIERY VENTILATION 

 The Principles of Colliery I 'entilation. By Alan Bagot, 

 Assoc.M.Inst.C.E., &c. (London: Kegan Paul, Trench, 

 and Co., 18S2.) 



DURING the last ten years, or, ever since it has 

 become necessary for colliery managers to obtain 

 certificates of competency by examination, there has been 



