226 



HARDWICKE'S SCIENCE-GOSSIP. 



herbivorous and graminivorous animals, especially 

 those of the elephant tribe. In these, the hard 

 enamel and the softer dentine and cement are arranged 

 in perpendicular or nearly perpendicular laminae, edge 

 up ; so that as the grinding work of the tooth proceeds, 

 its face shall wear unequally, and thus never become 

 smooth, always retain its serrated structure without 

 the chipping demanded by the miller's grindstones. 

 Mr. Ranyard's roadway is similarly made up of per- 

 pendicular plates ; the hardest compact, Portland 

 cement, with alternate plates of a softer mixture of 

 cement and sand. Both will wear, of course, but as 

 the latter will wear rather faster than the harder 

 cement, a ridge and furrowed face will be maintained 

 as long as the material lasts. 



To avoid jolting, these ridges and furrows must be 

 narrow. A quarter of an inch for the ridge, and three- 

 quarters for the furrow, are named. Regarding the 

 subject from a merely speculative point of view, I 

 cannot help fearing that the quarter inch will be too 

 narrow for steady wear ; but this, of course, is merely 

 a matter of practical detail, which can only be 

 determined practically. If three or four times as 

 thick, the jolting would be barely perceptible. 



Silver in Volcanic Ash. — Professor Mallet has 

 found that volcanic ash collected on the Pacific 

 coast in Ecuador, about 120 miles west of the volcano 

 of Cotopaxi, contains one part of silver in 83,600, and 

 that this exists probably in the form of silver chloride. 

 This amounts in value to about £\ sterling for every 

 ten tons. The ash is several inches in thickness, and 

 this presents a commercial problem. Chloride of 

 silver is dissolved by strong brine, and reprecipitated 

 by simply diluting the solution. From this preci- 

 pitate, pure silver is very easily obtained. Probably half 

 the chloride might be washed out by simply passing 

 brine through the ash. We are told that the whole 

 of the ash fell on one day, July 23, 1885. 



Munchausen Science. — I referred the extract I 

 made under this heading, to readers of this magazine 

 who " have sufficient knowledge of natural history to 

 form their own estimate of its veracity," and am glad 

 to learn that it has brought forth some response. Two 

 writers have (see pp. 203 and 213 last number) taken up 

 the subject. J. S. describes the extract as "a slightly 

 altered quotation from Kingsley's ' Glaucus ' " and 

 G. E. D. as " in the main an extract from ' Glaucus.' " 

 Kingsley states " three — six — nine " feet as the length 

 of the worm, the writer I quoted stretches this to 20 or 

 30 feet, which appears to me to be rather more than a 

 slight alteration of Kingsley, or of the " six to eight 

 feet" estimate of J. S. It is not merely a description 

 of a larger specimen, larger in all dimensions, but a 

 monstrous elongation of a phenomenally long creature, 

 only one-eighth of an inch diameter. 



The elephant Jumbo was, as nearly as I can 

 remember, a little more than nine feet high. What 



should we have said of Barnum, had he described it 

 in his show-bills as 20 or 30 feet high ? Are natural- 

 ists to be allowed more licence than we permit to the 

 advertising showman ? 



I read " Glaucus " when it first appeared, was then 

 much engaged in constructing and stocking aquaria, 

 and studying " the wonders of the shore." I found 

 that Kingsley's descriptions of many things were very 

 highly coloured ; pretty stories founded on fact. The 

 Parisian zoologists, referred to by G. E. B. , evidently 

 viewed them as I did. A still more highly coloured 

 version, with more than twofold and threefold magni- 

 fying, put forth as " Popular Science " surely deserves 

 the title I suggested. 



Granite. — The interesting "Notes on Granite," 

 by Mr. Fleck, in last number, remind me of some 

 remarkable examples of granite veins in granite 

 which I observed many years ago in the course of an 

 exploration of that remarkable geological microcosm 

 the island of Arran. Ascending Goatfell from 

 Brodick, by following the ravine of a small' torrent, 

 a well-known landmark, called " the mill dam," is 

 reached. Hereabouts are exposed good sections of 

 the coarse granite, intersected by veins of granite of 

 vairous degrees of fineness ; the thinner the vein, the 

 finer the granulations. The weathering of the course 

 granite is also well displayed ; the stream carries 

 away the nearly impalpable weathered feldspar, leav- 

 ing behind the crystals quartz almost completely 

 separated. This locality is well worthy of a visit 

 by those who are studying the vexed question of the 

 origin of granite. Having lost or mislaid my notes of 

 the trip, I cannot speak positively to details ; but, if I 

 remember rightly, there are thin veins of granite 

 running into the thicker veins. 



A Magnetic Oil Filter. — A curious invention is 

 described in " Engineering " as hailing from Chicago. 

 As everybody must have observed, the oil used for 

 lubricating machinery, soon becomes black, and 

 thickens at the same time. It is evident that the 

 blackening must be due to minute particles of iron 

 that are worn away from the bearings, in spite of the 

 lubrication. The same occurs to the oil on an oil- 

 stone used for sharpening tools. If these minute 

 particles were in water, or exposed to air, they would 

 speedily become red oxide ; but, protected as they are 

 by the oil, they proceed no further than the black or 

 magnetic oxide, or may even remain metallic. The 

 invention in question is based on this. It is an oil 

 filter for cleaning the oil that has thus been defiled 

 and thickened in doing its duty as a lubricant. It 

 consists of a vessel contracted in the middle and 

 surrounded at this part by a coil of wire through 

 which an electric current is passed. Iron filings 

 placed on the contraction are magnetized by induction, 

 and pick up the minute particles of iron or magnetic 

 oxide. The oil is further filtered mechanically by 



