December 12, 1912] 



NATURE 



411 



The Investigation of Flint. 



The need for a more accurate knowledge of the 

 dynamics of flint, as pointed out by Sir E. Ray 

 Lankester in Nature of November 21, is very obvious. 



Though not so remarkable as the Savernake polished 

 llints, yet some are to be found in the shingle for 

 some miles both east and west of Brighton. I-^lints, 

 too, with even more glaze than either of these are 

 met with on the arable land of this district. These 

 I assume got at some time the benefit of the vegetable 

 ash resulting from the burning of weeds, being raked 

 up along with them. Originally they came in the 

 chalk from the North Downs for the use of the crops. 



A caution may be useful as to what may be expected 

 as the result of frost action. I have watched many 

 of our Wealden sandstones for about twenty years, 

 chiefly because of my study of the honeycomb weather- 

 ing. One wall I guess at least 100 yards long, on the 

 west side of Mount Pleasant Hill, has soil behind it 

 nearly to the top. It shows good dusty weathering 

 along a line about 2 ft. from the pavement at the 

 junction of the second and third courses of stone. 

 There are, however, two very distinct patches, each 

 two or three yards wide, where this is entirely absent. 

 Whv is this? Merely, I believe, because the places 

 happen to get extra rain-water from two adjoining 

 trees, and are never dry all the winter. Parts, how- 

 ever, which are wet and dry alternately frequently 

 suffer. 



Why, I wonder, is it that the small mammilations 

 seen on the squared flints of the churches in the 

 eastern counties are absent in the southern counties? 

 Again, the Norfolk paramoudra deserve more study 

 than they have had hitherto. This year at Seaford 

 I found a 2-in. layer of chert at the top of the 

 chalk, which I was told is usual there. The explana- 

 tion seemed to be that rain-water had taken up silica 

 from the overlving sands and gravels. On the west 

 of Cuckmere Haven the chalk cliffs have also remark- 

 able rings of chert, sometimes 6 in. thick, surround- 

 ing each of the numerous pipes seen in the chalk 

 there. These chert cylinders can be seen lying on 

 the shore owing to the erosion by the sea. For a 

 long time these were great puzzles, but their explana- 

 tion was discovered last year b\' mv friend, Mr. Hy. 

 Preston, of Grantham. George Abbott. 



Tunbridge Wells, November 23. 



Remarkable Formation of Ice on a Small Pond. 



Some soil (which is of a heavy nature), being re- 

 quired, had been dug out to a depth of about a foot. 

 The sides and bottom were thus quite irregular. 

 Rain-w-ater lodged in the hole, thus forming the pond, 

 which was about 4 ft. long, i ft. 6 in. wide, and 5 in. 

 maximum depth; the major axis was N.E. and S.W., 



H-!i'^ 



and the upper surface of the ice about S in. below 

 the general level of the ground. 



The ice was first noticed at 0.30 p.m. on Sunday, 

 December i. Dark sinuous lines about § in. wide and 

 running about parallel to the major axis were plainly 

 visible. These were seen to be due to the water below 

 touching the ice along these lines, while the bands | 



NO. 2250, VOL. 90] 



(about 2j in. wide) of white between the lines were due 

 to the water not being in contact with the ice at these 

 portions of the under-surface. The water in the pond 

 had gradually percolated away, and had thus left an 

 air space of about \ in. between itself and the under- 

 surface of the ice between the dark lines. On break- 

 ing the ice and getting a piece out, it was found to 

 have the remarkable cross section shown in the sketch. 

 The ice was quite clean and clear, and the dovetail 

 ribs were well off the bottom of the pond. The ribs 

 were remarkably regular in form and dimensions, 

 and there were about six lines of them running from 

 end to end of the pond. 



There was no wind, and the frost on the grass near 

 by was crisp, indicating that the temperature was still 

 below 32° F. 



A. S. E. ACKERiMANN. 



Anthropology at the British Association. 



I NOTICE in the article on anthropology at the 

 British Association in Nature of November 21 a 

 slight misstatement, which I should be obliged if you 

 would correct. 



The coloured photographs which I showed to the 

 section were taken partly by my friend Mr. Mellor and 

 myself, and the scenes represent dififerent tombs which 

 I excavated in 1903-05. Robert Mond. 



Combe Bank, near Sevenoaks, November 25. 



ATMOSPHERIC ELECTRICITY. 

 TOURING the last few years a large number 

 -L^ of experiments and observations have been 

 made which, instead of solving the central problem 

 of atmospheric electricity, appear to have made it 

 more difficult than ever. It seems desirable, there- 

 fore, that a short statement of the present position 

 should be placed before the large body of physic- 

 ists who have not yet considered this exceedingly 

 interesting subject. 



Measurements of the electrical conditions of the 

 atmosphere have now been made over the land 

 from north polar regions through the equator to 

 south polar regions, over the centres of the 

 Atlantic and South Indian Oceans, and on Samoa 

 in the Pacific Ocean. Thus the conditions over 

 both land and ocean areas have been investigated, 

 and everywhere it has been found that the air 

 is a conductor and that the potential gradient is 

 practically the same. The result can be expressed 

 in rather a more objective way by stating that 

 the earth has been found to be a negatively 

 charged sphere, of a nearly uniform surface 

 density, surrounded by a conducting atmosphere. 

 This, however, cannot be a complete statement 

 of the case, for by the laws of electrostatics a 

 charge cannot exist within a conductor, and in 

 consequence the charge on the surface of the earth 

 must be transferred more or less quickly to the 

 outside of the conducting atmosphere. In spite 

 of this, the charge on the earth's surface remains 

 undiminished. Whence, then, comes the negative 

 charge to make this possible? This is the chief 

 problem of atmospheric electricitv. 



To make it clear that the surface of the earth 

 does lose electricity, it will be as well to state 

 the methods used to determine the loss. The 

 surface of the earth is at a uniform potential, which 



