July, 1912. 



KNOWLEDGE. 



273 



The week ended June 1st was fine and dry at first, but the 

 weather became showery and thunderstorms occurred. Solar 

 haloes were observed on the 26th. Temperature was below 

 the normal generally, but in Scothind, W., and the English 

 Channel it was slightly in excess. The highest readings 

 reported were 77° at Greenwich and 

 Camden Square on the 30th, with 74° at 

 Norwich, and 73^ at Kaunds. The lowest 

 of the minima were 29° at Llangammarch 

 Wells on the 26th. 30° at Bahnoral on the 

 27th, 31° at West Linton, and 32° at 

 Cohnonell on the 26th. At no other 

 station besides the four just named was 

 frost recorded in the air at four feet 

 above ground. On the grass the lowest 

 readings were 24" at Greenwich and 

 West Linton, and 25° at Crathes. The 

 temperature of the soil at one foot depth 

 was below the average in most places, 

 while at four feet depth it w.is still in 

 excess. 



Rainfall was more than usual in England. 

 N.IC, the Midlands and the English 

 Channel. In England, S.E., it was just 

 normal, but in all other districts it was 

 in defect. In Scotland, E., the tot.il was 

 less than one quarter of the usual amount, 

 and in Scotland, N., just over one-third. 

 The number of rain-days over the whole 

 kingdom agreed with the average. 



Sunshine was above the average in 

 England, S.E., N.W., S.W., Ireland, S.. 

 and the English Channel; it was equ;il 

 to the average in Ireland, N., but below 

 the average elsewhere. In England. N'.E.. 

 the mean daily amount was only 3-8 hours 

 (23%). In the English Channel it was 

 10-4 hours (66"o). Of individual stations 

 Baltasound. Shetland, reported a daily 

 average of 1-4 hours (8%) while Wey- 

 mouth had 11-6 hours (73%). At West- 

 minster the average was 7-2 hours (45%l, 

 while Hampstead had 

 8- 1 hours (51"o). The 

 temperature of the sea 

 water ranged from 46° 

 at Lamlash to 59° at 

 Eastbourne. 



The we.ather of the 

 week ended June 8th 

 was very unsettled with 

 much rain and many 

 thunderstorms. Tem- 

 perature was low tor 

 the time of year, ever\ 

 district reporting values 

 below the normal. The 

 maxima were unusually 

 low. At only four 

 stations were readings 

 of 70° or upwards re- 

 corded, namely at 

 Camden Square and 

 Plymouth 71°, and at 

 Greenwich and Tot- 

 tenham 70° ; these all 

 occurred on the 6th. 

 The lowest readings, 

 however, were not as 

 low as in the previous 

 week, the minimum being 32° at Balmoral. The next lowest was 

 33° at Killarney. In .Scotland, N.and E., with the exceptions of 

 32" at Balmoral already mentioned and 39° at Strathpeffer the 

 minimum nowhere fell below 40°. At Leith and at Guernsey 

 the lowest readings were the same, 48°. On the grass the 

 lowest readings observed were 29° at Balmoral and 31° at 



C 1) 



Figure 302. Trans-section of a Brazilian liana 



Greenwich. The teinperature of the soil, both at one foot and 

 at four feet depths was below the average very generally. 



Rainfall was slightly below the average in Scotland N., but 

 was in excess in all other districts, and very greatly so in 

 some. Thus in the English Channel the total for the week 

 was 2-15 inches as compared with an 

 average of 0-44 inches, or almost five 

 times as much as usual. In Jersey it 

 rained each day throughout the week, the 

 total collected being 2-85 inches. At 

 Harrogate the total was 3-20 inches, 

 though at that station there were two 

 days on which no rain fell. 



Sunshine was in defect in all districts, 

 and at each individual station except 

 Valencia and Markree Castle. Valencia 

 was the sunniest station with a daily 

 average of 7-6 hours (47%). At Glasgow 

 the daily mean was only 0-9 hours (5%). 

 In Westminster the daily average was 

 5 • 2 hours (32%). 



The temperature of the sea water ranged 

 from 47° at Berwick to 62° at Margate. 



THE SPRING.— The period of thirteen 

 weeks, March 3rd to June 1st, which is 

 regarded from a meteorological point of 

 view as Spring, was this year on the whole 

 warm and dry, with an a\erage amount 

 of sunshine. In England, S.E., of the 

 thirteen weeks seven were unusually warm, 

 one unusually cold and five not far from 

 a%erage ; two weeks were very wet, five 

 weeks very dry and in six weeks the rainfall 

 was about normal; while six weeks were 

 unusually sunny, three weeks unusually 

 dull, and during four weeks the sunshine 

 was moderate. 



MICROSCOPY. 



By F.R.M.S. 

 POWER PHOTO-MICRO- 

 GRAPHY. EQUIVA- 

 LENT EXPOSURES. 

 — One of the great 

 troubles of the inexperi- 

 enced worker in this 

 fascinating branch of 

 work is the problem of 

 equivalent exposures 

 with different lenses and 

 stops, and so on. But 

 I think the matter may 

 be put in such a simple 

 form that not only can 

 it be easily understood, 

 but what is perhaps of 

 still greater practical 

 importance — easily re- 

 membered and carried 

 out in practice. 



First, let us take the 

 case of a fixed camera, 

 length say twelve inches 

 (objective to plate), and 

 the same numerical stop 

 number, e.g., /.ll. 



I have four lenses 

 whose focal lengths are 

 four, three, two and 

 four-fifth inches respectively. What are the equivalent 

 exposures for the same object, lighting, camera length and 

 stop ? 



Theoretically it may not be quite correct to say that 

 exposure varies directly as area magnification or the square of 

 linear magnification, but in practice this rule works quite well. 



LOW 



