August 1, 1884.] 



SCIENCE. 



99 



seen by obtaining the electrical discharge in 

 different gases, such as carbonic-acid gas or 

 nitrogen, and comparing these photographs 

 with those taken in free air. Although we can 

 study certain phenomena of atmospheric elec- 

 tricity successfully in our laboratories, yet we 

 cannot charge a cloud with positive electricity, 

 and fill the sky with different strata of hot and 

 cold air. It is generally believed to-day among 

 scientific men, that the electricity of thunder- 

 storms cannot be attributed to sudden evapora- 

 tion or condensation of moisture ; for direct 

 experiment has failed to reveal any electricity 

 which is due to these causes. Mr. Freeman 

 made many delicate experiments in the physi- 

 cal laboratory of Johns Hopkins university 

 to decide the question whether evaporation 

 produces electricity, and he could find no evi- 

 dence of any that was due to this cause. Herr 

 Kayser has also lately experimented at the 

 physical laboratory of Berlin upon the elec- 

 trical effects of condensation, with negative 

 results. Personally I feel that all the experi- 

 ments hitherto conducted on the electricity due 

 to evaporation and to condensation have been 

 conducted on too small a scale to test the 

 question ; and I do not see how the}' can be 

 conducted on a larger scale. When we think 

 of the immense plan upon which these opera- 

 tions are conducted in nature, of the evapora- 

 tion from ever} T square foot of the ocean, and 

 of the rapid condensation through miles of 

 space, we can realize that an infinitesimal 

 amount of electrical charge, too small to be 

 detected in a laboratory, might be integrated 

 into a large amount, and, becoming localized, 

 might produce the tremendous electrical dis- 

 turbances which we witness in thunder-storms. 

 How, then, can we conduct future inves- 

 tigations upon thunder-storms? The most 

 promising direction for scientific work seems 

 to be in the establishment of systematic obser- 

 vations on thunder-storms, and on atmospheric 

 electricity in general, over a large tract of 

 country. In certain regions, thunder-storms 

 follow certain definite paths, and other tracts 

 are never visited by them. There is a general 

 impression that electrical storms are, in com- 

 mon language, attracted by rivers, and are 

 more severe about large bodies of water in 

 general. However this may be, nothing but 

 systematic daily simultaneous observation, long 

 continued, can increase our knowledge. If 

 the government, in connection with the signal- 

 service, should establish a number of electrical 

 stations throughout the west and south, where 

 thunder-storms and tornadoes are so frequent, 

 daily thunder-storm maps might be issued, 



showing the probable path of the electrical dis- 

 turbances. Perhaps we should then see, in 

 districts peculiarly infested by thunder-storms, 

 certain ' insurance-against-danger-by-lightning 

 retreats,' in which Benjamin Franklin's light- 

 ning-rod should rise from a small hut, com- 

 pletely covered with a network of metallic rods 

 which are connected with running water or a 

 large extent of moist earth. These safe re- 

 treats would certainly be a great desideratum 

 for many who now suffer greatly from nervous 

 terrors during thunder-storms. 



John Trowbridge. 



THE FORMATION OF CANONS AND 

 PRECIPICES. 



One of the most remarkable natural objects 

 in the state of New York is to be seen at the 

 crossing of the Genesee River, at Portage 

 station, on the New- York, Lake Erie, and 

 western railroad, 362 miles from New- York 

 City, and 83 from Buffalo. The railway here 

 spans a deep gulf on an iron bridge 820 feet 

 long and 235 feet high, near the upper end of 

 a wonderful canon. There are three falls 

 of the river immediately below the bridge, 

 measuring 60, 90, and 110 feet respectively. 

 The gorge runs out in the Genesee shales at 

 Mount Morris, being 20 miles long by the 

 meanderings of the river, which falls 500 feet 

 in that distance. In some places the banks 

 are 350 feet high, nearly perpendicular, and 

 the ravine is wholly impassable. It is a fine 

 example of the work of water ; and there are 

 hundreds of others in that state, on a smaller 

 scale, in the upper part of the Portage group. 

 One of these is the celebrated Watkins Glen, 

 a beautiful canon two miles long, with a suc- 

 cession of cascades. The neighboring glen at 

 Havana is very similar ; and there are a number 

 of others farther north, several of which may 

 be seen at Big Stream, Rock Stream, Dresden, 

 and other places. Taghanic and Lodi Falls. 

 and the glens and ravines about Ithaca on 

 Cayuga Lake, and man}- other similar places. 

 are all on the Portage formation, which forms 

 a narrow east and west band across western 

 New York. It might be added, that both 

 Seneca and Cayuga Lakes are, in part at least, 

 simply old Portage glens, now filled with water. 

 To many reflecting persons who. as summer 

 tourists, visit these very curious and beautiful 

 resorts, the thought occurs, why these canons 

 are in these particular places above all others, 

 and how the}' have been caused, the work of 

 glaciers, or some convulsion of nature, being 



