April 6, 1888.] 



SCIENTIFIC NE\VS. 



333 



sphere whose winter occurred in aphelion. Professor 

 Claypole went on to point out new facts which had come 

 to light which tended to disprove this theory, which lor 

 fifteen years had been very favourably received. Accord- 

 ing to Croll's theory the glacial period, calculating from 

 astronomical data, extended from 240,000 to 80,000 years 

 before 1800 a.d. Professor Claypole argued that the 

 rate of recession of the Falls of Niagara, owing to 

 the erosion of the water, would give 15,000 years as the 

 age of the gorge below the Falls, which was between six 

 nnd seven miles long, and had probably been receding at 

 a tolerably uniform rate since the end of the Ice Age. 

 Again, the Falls of St. Anthony, on the Mississippi, were 

 at the head of a gorge seven miles long, and their rate of 

 recession gave an age of 8,859 years to the gorge, which 

 was entirely post-glacial in age. Professor Claypole 

 accordingly saw no possibility of maintaining an antiquity 

 of 80,000 years for the final retreat of the Ice from the 

 St. Lawrence and the Upper Mississippi valley, and he 

 concluded that the Ice Age ended 10,000 or 15,000 years 

 ago. If that were so, the cold could not have been 

 due to increased eccentricity, as Dr. Croll contended. 

 Mr. Hugh Miller gave some observations on a dust storm 

 which he had witnessed in Eastern Ross. After a pro- 

 longed drought last summer, he had seen in June the 

 dust from the turnip fields and fallow land flung up in 

 dense clouds, as a kind of intermittent stream, which 

 spread a pale brown haze over the whole district, not less 

 than three or four hundred feet in depth in some places. 

 The occurrence led to the remark that, except for the 

 binding influence of vegetation, wind must rank as one 

 of the most powerful geological agents. He gave 

 instances of the wasting of cliffs to sand, the destruction 

 of soils, and the slow disintegration of crags through 

 this means. Dr. W. G. Black exhibited a new clino- 

 meter, which consists of a hollow hemisphere divided ' 

 internally into degrees, and enclosed in a small box. 

 When the box is set down on a stratum, a pellet inside 

 the hemisphere indicates by its position the inclination 

 of the stratum. 



EDINBURGH FIELD NATURALISTS' SOCIETY. 



At the meeting, on February 22nd, Mr. William 

 Penman communicated a paper on the " Polar Dark- 

 ground Illumination," and Mr. John Lindsay read a 

 note on an " Ancient Lake Deposit in Queen's Park," 

 which had been uncovered by recent operations in form- 

 ing a new main drain there. From 3 ft. to 10 ft. of a 

 superficial deposit and natural soil was first cut through, 

 then a yellow clay, from i ft. to 4| ft. thick; next a layer 

 of peat, varying in thickness from i ft. to 14^ ft., and 

 immediately underneath was the shell marl, from 5 ft. to 

 9 ft. thick. The marl was studded with countless 

 myriads of fresh-water shells belonging to the genera 

 Limnce, Valvata, Planorbis, and Cyclas. Of some of these 

 genera there were several species. The shells were very 

 light, and extremely brittle. The lake must at one time 

 have been very extensive, probably coming close up to, 

 if it did not cover, the site of Holyrood Palace. 



MANCHESTER SCIENTIFIC STUDENTS' 

 ASSOCIATION. 



At the meeting held on the i8th ult., Mr. R. Cobden 

 PhiUips delivered a lecture on the " Lower Congo," 

 illustrated by views. 



CORRESPONDENCE. 



The Editor does not hold himself responsible for opinions expressed 

 by his correspondents^ nor can he take notice of anony?nous com- 

 munications. All letters must be accompanied by the 7iame and 

 address of the writer., not necessnrily for publication, but as a 

 guarantee of good faith. 



THE ELECTRIC ACTION OF LEAVES. 



In the Scientific News a correspondent seeks to explain 

 the saw-like structure of the edges of the leaves of grass 

 and of certain other plants by a " final cause." He refers 

 to the well-known fact that electricity finds either ingress 

 or egress by points more readily than by blunt, rounded 

 masses. From this fact he draws the inference that leaves 

 are able to draw off silently any accumulation of elec- 

 tricity, either in the soil beneath or in the clouds above, and 

 thus prevent, or at least mitigate, violent lightning-strokes, 

 whether ascending or descending. To decide upon the reality 

 of this alleged action it would be necessary to make extended 

 observations upon the incidence of thunder-storms. Are they 

 more severe over seas, lakes, desert plains, etc., where there 

 is, of course, an absence of vegetation, than over woods, 

 prairies, or cultivated lands ? 



The question may also be raised whether it is legitimate to 

 explain any peculiarity in the structure of a plant or an animal 

 by reference to the supposed influence such peculiarity may 

 have upon some other being. Z. Z. 



GENERALISED PORTRAITS. 

 Your readers are, of course, aware of certain interesting 

 results obtained bv means of "generalised photographs." 

 Thus, at the great Canadian meeting of the British Associa- 

 tion, such portraits respectively of the naturalists and the 

 physicists present, showed decidedly different types of head. 

 Now it strikes me that a generalised portrait of the quack 

 would be of no small value. This gentleman lias become of 

 late very fond of adorning his advertisements with a represen- 

 tation of his "refined and intellectual countenance," and it 

 strikes me that I can in such portraits delect some common 

 features. Phos. 



HEIGHTS OF WATERFALLS. 

 A paragraph given on p. 200 of the Scientific News makes 

 no mention of the Falls of the Parana. That at Iguazu is 

 calculated at 174 to 180 feet, being 30 feet higher than the 

 Niagara. Its breadth is 1,000 yards, and its volume of water is 

 enormous. The Guaira Fall en the same river is much larger 

 still. S. T. 



Etching on Boxwood Blocks. — ^From the Photo- 

 gmphisches Archiv we learn that in Russia a new 

 method of producing etchings on boxwood blocks 

 for wood engraving has been invented. The pores 

 of the block are first filled with insoluble carbonate 

 of copper, by means of two separate solutions, in which 

 it is iDoiled sufficiently. The surface of the block is then 

 polished, and asphaltum in solution applied to its back 

 and sides. Finally, the polished face is coated with a 

 film of bichromate gelatine. The block is then exposed 

 under a negative, and the unaffected and soluble parts of 

 the bichromate gelatine are removed by washing. The 

 raised parts are next coated with an asphaltum solu- 

 tion, the block is immersed in a strong solution of nitric 

 acid for about an hour, and is removed and subjected to 

 the action of sulphuric acid for the same period. The 

 parts unprotected are thus changed to nitro-cellulose, 

 which, by brushing, is readily removed in the form of a 

 greenish powder. Finally, the block is dried, and briskly 

 rubbed with a stiff brush. Then the asphaltum is dissol- 

 ved and removed by benzine, and the block is ready for 

 printing. The invention is an ingenious one, and we shall 

 be glad to hear that its practical application is successful. 



