92 



NA TUBE 



[Nov. 



1886 



along the coast of Norway, and may be traced even to 

 Spitzbergen. 



Another equally interesting illustration of the mildness of 

 the winter in Norway is shown by two diagrams of the 

 "thermal anomaly" in January. By way of comparison the 

 month of July is included. It may be added that by thermal 

 anomaly is meant the difference which exists between the tiiie 

 mean temperature of a place and the mean temperature actually 

 fegistered m that latitude. 



In January the thermal anomaly is very remarkable. Thus, 

 along the coast of Norway, between the northernmost and 

 westernmost promontories, the North Cape and Stat, it reaches 

 + 20° C, and in the sea outside most probably + 25° C. These 

 figures are certainly very remarkable. Eastwards, it decreases 

 inland, but even here — where the cold is very great in the 

 winter — it never falls below + 7°. In the Baltic, on the other 

 hand, it again rises, as might be expected. 



In the summer, however, the conditions are far from being so 

 favourable. There is, indeed, then a narrow strip of land, on 

 the very verge of the coast, where the thermal anomaly is 

 slightly nig;a/h'e. The line for the 0° C. anomaly then follows 

 the west coast, decreasing gradually seawards, whilst eastwards, 

 across Southern Norway, it rises to + 4° C, and in Finmarken 

 to + 70° C. 



For the further elucidation of this, the following comparison 

 of the January mean temperature in various places on the globe 

 in about the same latitude may serve : — 



Ahmt 60° N. lat. 



Helliso Lighthouse... ... ... ... ... 2 



Bergen ... ... ... ... ... ,. o 



Christiania ... ... ... ... ... ... - 5 



Stockholm ... ... ... ... ... ... - 3 



St. Petersburg ... ... ... -10 



Jakutsk ... ... ... ... ... ... -42 



North Kamchatka ... ... ... ... ... -20 



South Alaska ... ... ... ... ... —20 



Great Slave Lake ... ... ... ... ... -25 



North Coast of Labrador ... ... ... ... -25 



Cape Farewell ... ... ... - 7 



Shetland Islands .. ... ... ... ... 4 



About 71° N. lat. ^ 



North Cape... ... ... ... ... ... - 4 



South Novaya Zemlya ... ... ... ... -20 



Mouth of the Yenisei 



Mouth of the Lena 



Point Barrow 



Boothia ... ... ... ... ... ... -32 



Upernivik ... ... ... ... ... ... -20 



Jan Mayen ... ... ... ... ... ... - 10 



The coldest place on the globe where the mean temperature 

 has been exactly ascertained, viz. Werchojansk, in the interior 

 of Siberia, with - 48° C. in January, lies in the same latitude 

 as Bodo, where it is - 2° C, and Rost, with o°-5 C. 



In order to obtain correct normal values of the temperature 

 in a place, long and continuous series of observations are neces- 

 sary ; and when we consider that the longest we possess for any 

 place only extends over 100 years, and that meteorology is but 

 a science of yesterday, the Norwegian meteorological records 

 can make a fair show. With regard, however, to the changes 

 which take place in the climate in a certain spot during ages — 

 which occurrence is beyond dispute — we have no reliable data. 

 I will only mention here Prof. Blytt's theory, ' which has attracted 

 many supporters, viz. that the periodical changes in the climate 

 are due to the precession of the equinoxes (with a mean period of 

 about 21,000 years), and to changes in the eccentricity of the 

 earth's orbit. 



It is, however, possible to accept a shorter periodical change 

 in the climate than this, and theories on this point have not been 

 wanting ; but the only one which has found any support is the 

 eleven-year period, corresponding to that of the sunspots, which 

 again coincides with that of the terrestrial magnetic phenomena. 

 It has even been attempted to bring the fall of rain and snow 

 within a certain law, and, as some maintain, with success ; 

 but in my opinion the proofs advanced in support of such a 

 theory are far from being conclusive. 



-34 

 -40 



» Cf. Prof. Darwin's Address to the Bri 

 Nature, vol. xx.\iv. pp. 220 and 239. 



1 A; al 



TO PROVE THAT ONLY ONE PARALLEL CAN 

 BE DRAWN FROM A GIVEN POINT TO A 

 GIVEN STRAIGHT LINE 

 (l) T ET OP and OQbe two lines at right angles, and let 

 p Q move along them from o, so that O P always 

 = o Q. Then P Q always > o Q or o P. 

 Hence if O Q increase without limit, P Q must also do so. 

 Let o N bisect the angle r o Q. Then N bisects P Q. 

 Then if o Q increase without limit, Q N does so (q N = 



If o q' be taken along o N = O Q, Q Q' > Q N. 



Hence if o Q increase without limit, Q Q' does so. 



Similarly by bisecting q'oq by o M, we can show that QM 

 increases without limit with o Q, and so on by continual 

 bisection. Hence — 



If two straight lines meet at any angle, the perpendicular from 

 a point of one on the other becomes infinite when that point 

 is at infinity. 



(2) Let OQ be some given length taken at right angles to a 

 line o P ; 



Let P R move along o P at right angles to o r, so that P n 

 always = o Q. 



Join Q R, QP. 



Let o P increase without limit. 



Then the angle P r tends to become zero. 



For the lines n r, pq never become infinitely separated. 



Thus there is evidently some definite position for the line Q P 

 when o V becomes c« . 



(3)Let a line PQ move at right angles to OP, so that P Q = 

 o P. 



Then if o P increase without limit, o Q increases without 

 limit. 



Hence, there is some finite angle, Q o P, such that the perpen- 

 dicular Q p from Q at cc on o P falls at an infinite distance from o. 



The same thing is evidently true for all angles less than Q o P. 



Then either it is true of all angles less than a right angle, in 

 which case it can be easily shown that only one parallel can be 

 drawn from a given point to a given line ; 



Or, there is some limiting angle, Qo p, for which n p falls at 

 CO , and for any greater angle (< right angle) Q v falls at some finite 

 distance from o. 



