640 TEANSACTIOJ^S Oi-' SECTION A. 



compounds titaiiiunl-oxide aud magnesium hydride are iudubitablypveselit, CaiiSed 

 Ijy the expansion of the escaping vapours, is sufficiently great to permit tb« 

 combination of the oxygen and hydrogen to form water-vapour in the state of 

 superheated steam. 



5. Sun-spots and Solar Temperature. 

 By Professor E. T. WhittakeR, Sc.D., F.R.S. 



Tlie majority of astrophysicists incline to the view that sun-spots are places of 

 diminished temperature ; this view is based on the observational evidence, which 

 is (i) that chemical compounds are present in spots, (ii) that the ' arc ' lines are 

 widened and the characteristic ' spark ' lines weaken'^d in the spot-spectrum 

 as compared with the ordinary Fraunhofer spectrum, and (iii) that the con- 

 tinuous background of the spot-spectrum has its maximum displaced towards 

 the infra-red as compared with the continuous background of the Fraunhofer 

 spectrum. 



The writer observed with regard to (i) that the formation of chemical com- 

 pounds from their dissociated elements may be brought about either by a fall of 

 temperature or by a rise of pressure ; with regard to(ii), that the observations of 

 ihe high-level and low-level chromospheric spectrum show that ' arc ' lines are 

 .issociated with the high pressures of the lower chromosphere rather than with 

 the low temperatures of the upper chromosphere; and with regard to (iii) that 

 the differences between the continuous spectra of the spot and of the rest of the 

 sun is analogous to the difference between sunlight as observed at noon and 

 near sunset, the difference being in this case due to the extra depth of atmosphere 

 through which the sunlight has to travel. It is concluded that the phenomena 

 of the spot-spectrum are to be ascribed to relativelj' high pressure rather than 

 to relatively low temperature. 



6. Recent Researches on the Cause of Seiches. 

 By E. M. Wedderburn, F.R.S.E. 



In the autumn of the year 1905 careful observations were made in Loch Earn 

 by Professor Chrystal which throw much light on the effect of meteorological 

 conditions on the denivellations of lakes. In addition to the three stationary 

 liranographs employed to record the seiches, Dine-Shaw microbarographs were 

 stationed at Ardtrostan (on Loch Earn), Loch Earnhead, and Killin (on Loch 

 Tay), There was also at Ardtrostan a pressure anemograph. By means of the triad 

 of microbarographs an indication could be obtained of the rate and direction of 

 travel of the disturbances shown on the traces. Out of twenty-seven cases 

 I'xamined by Professor Chrystal, the disturbances travelled in a S.W. direction 

 in twenty-two cases, and in a N.E. direction in five cases. The average velocity 

 of propagation was about thirty miles per hour. 



Comparison of observations in Lochs Earn, Treig, Ness, Lubnaig, Tay, and 

 Garry (Inverness-shire), indicate that seiches are most frequent in lakes which are 

 deep and straight, and also in those which run in the direction in which the 

 microbarometric disturbances travel. 



Possible causes of seiches, mentioned by Professor Chrystal, are as follows, 

 viz. : — 



(1) Earthquakes. The evidence from Loch Earn and Loch Ness is that 

 earthquakes are not an effective cause of seiches. Against this must be set the 

 great disturbances which are said to have occurred at the time of the Lisbon 

 earthquake of 1755. 



(2) Progression of the general system of isobars causing a release of static 

 denivellation of the lake surface. Calculation shows that even in the most 

 favourable circumstances a seiche produced in this manner must be of very Small 

 amplitude. 



