578 REPORT — 1903. 



spectres est la meme. Dans le spectre cathodique vous voyez une ligne assez forte 

 dont la longueur donde est de 317 m. environ. Cette ligne ne se trouve pas dans 

 le spectre de I'aurore polaire. Mais dans I'hiver 1900-1901 M. la Cour, qui a fait 

 toutas les photographies spectralea en Islande, a trouviS cette ligne pendant iin 

 sejour en Finlande. 



Le spectre que j'ai I'honneur de vous avoir montre n'est pas le spectre complet 

 de I'aurore ; nous n'avons paa pu photographier des lignes dans la partie des spectres 

 dont la longueur d'onde est situe entre X - 557 m. et X = 470 m. La nature de la 

 ligne principale d' Angstrom a et6 inconnu jusqu'a ce dernier temps. "Vous savez 

 que M. le professeur Ramsay, qui a decouvert lui-meme le crypton, a constats 

 qu'une des lignes de cet air coincide parfaitement avec la ligne d'Angstrom. 



7. Discussion on Kite Observations continued. 



8. Diurnal Range of the Siommer Temperature of the Levant. 

 By Alexander Buchan, LL.D., F.B.S., F.R.S.E. 



One of the best portions of the sea in -which the effects of insolation and 

 nocturnal radiation on the temperature can be most satisfactorily investigated is 

 the Levant during the summer months, it being there and then that the sky is 

 cloudless, or all but cloudless, the air very dry, with little or no rain, and calms 

 or light winds prevalent, from approximately the same direction. 



It was under such favourable conditions that the four magnificent series of 

 serial temperatures were made in the summers of 1890, 1891, 1892, and 1893 

 respectively, by the Austrian ship ' Pola,' in the eastern half of the Mediterranean, 

 at various depths from the surface of the sea to the bottom. These have been 

 published in e.vtenso, together with the rest of the deep-sea work carried out by 

 the ' Pola,' in the ' Transactions of the Imperial Academy of Sciences of Vienna.' 



The thermometers and the other instruments used for salinity, colour of sea, 

 &c., were the best that could be procured, and nothing but the highest praise can 

 be passed on the methods employed and the skill with which the observations were 

 carried out and printed. 



With the temperature observations are also published the hours of the day at 

 which they were taken, and at the same time the temperature and pressure of the 

 air, the amount of cloud, and the direction and force of the wind. Hence a novel 

 and notable addition to science accompanies these observations, viz. the time of 

 day at which they were made. In truth this observation of time invariably 

 recorded throughout the four summers presents us with the means of arriving, for 

 the first time, at a knowledge of the depth to which the sun's heat penetrates so 

 as to aflect the temperature of the water, and also the amount of daily variation 

 brought about at different depths up to the surface by solar and nocturnal 

 radiation. 



To carry this out two tables were constructed. One table showed the observa- 

 tions made at those hours of the day which may be regarded as showing the effect 

 of insolation, and the table for the observations at the hours which may be 

 regarded as showing the effect of nocturnal radiation. The hours for insolation 

 were from 2 to 6 p.m., and the hours for nocturnal radiation in the morning till 

 9 A.M., the mean time of the fifty days for insolation being from 3.14 to 

 4.30 P.M., and of the fifty days for nocturnal radiation being from 6.30 to 

 7.45 P.M. In any one of these 100 cases the least depth of the sea at the place 

 where the serial temperatures were recorded was 419 metres, but generally the 

 depth much exceeded this figure, the depth in any case being 4,400 metres. 



For the fifty p.m. observations the mean position was 35° 29' lat. N. and 

 26° 24' long. E.; and for the fifty a.m. observations 35° 35' lat. N. and 

 26° 31' long. E. Hence the geographical positions were virtually identical, and 

 on no particular day was there any material difference between the two positions. 



