TRANSACTIONS OF SECTION A. 597 



To provide for the sphericity of the earth deductions of various amounts, 

 according to circumstances, were made from the numbers obtained from the 

 formula which Mr. Close had arrived at by a double process, and which is given at 

 Icufrth in the paper itself. 



Combinino: these results with those given above, we obtain as the whole rise of 

 the ocean surface as follows : — 



(1) Mexico, 780 feet; (2) Bolivia, 2,150 feet ; (3) Chile, 1,580 feet. 



In all the above cases the coast was taken as descending to a depth of 

 15,000 feet at a gradient of about :j\- to ^j-„ the comparatively low results in the 

 case of Chile being due to the narrowness of the mountain range, 30 miles in mean 

 breadth, as compared with 300 miles in the case of Bolivia. 



The above results, which are probably rather under than over estimates, fall 

 considerably short of those to be drawn from Suess and Fischer's formula, but are 

 probably much in excess of the views held by British physical geographers gene- 

 rally ; and the conclusion was drawn, that if the same processes of reasoning and 

 calculation were applied to all parts of the world, it would be found that the ocean 

 waters were piled up to a greater or less extent all along our continental coasts, 

 producing very important alterations in the terrestrial configuration as compared 

 with an imaginary ellipsoidal, or geodetic, surface, to which all these changes of 

 level must necessarily be referred. 



11. On some Variations in the Level of the Water tu Lale Oeorge, New South 

 Wales. By H. A. Russell. 



This paper refers to certain changes in the level of the water of Lake George, 

 as shown by the recording machine placed there. They consist : — 



(1) Of changes in tlie level of the water similar to those which have been 

 observed at the Lake of Geneva and other places with variations not yet accounted 

 for. 



(2) Of changes in level lasting several hours, for which no cause is apparent, 

 but which the author thinks may result from changes in the vertical like those 

 observed by Professor Darwin, M. D'Abbadie, and others. Reference is made to 

 the annual change in the level errors at Greenwich, Sydney, and other places, the 

 period of which coincides with that of the solstices, and to other changes in it per- 

 haps connected with those in the lake. 



(3) Of a diurnal change in level, not coincident with ocean or atmospheric 

 tides. In this change the water rises to its maximum at the south end of the lake 

 at noon, and its minimum at midnight. The amount of change varies, but does 

 not seem to be affected by the position of the moon. 



12. Oti the different kinds of Thunclerstorms, and on a Scheme for their 

 Systematic Observation. By the Hon. Ralph Abercrombt, F.B.Met.Soc. 



The author shows that there are at least three distinct types of thunderstorm in 

 Great Britain. 



The first, or ' squall thunderstorms,' are simply squalls associated with thunder 

 and lightning, which fly nearly with the surface wind. These form on the sides of 

 primary cyclones. 



The second, or 'secondary thunderstorms,' are associated with secondary cyclones. 

 These move against the surface-wind, and are very rarely accompanied by squalls. 

 Very little is known of the nature of these storms, though they are the commonest 

 type of thunder in Great Britain. 



The third, or ' line thunderstorms,' are apparently of a totally different nature. 

 They take the form of long narrow bands of rain and thunder — perhaps one hundred 

 miles long, and only five or ten broad, which cross the country rapidly nearly 

 broadside on. These are usually preceded by a very violent squall. The squall 

 which capsized the ' Em-ydice ' was of this type. The air in line thunderstorms 

 seems to circulate round a long horizontal axis — which would lie in the direction 



