Nov. 25, 1880] 



NATURE 



93 



grate, viz. : — (l) the gas-pipe (d) with holes of about I's inch 

 diameter, i"5 inch apart along the upper side inclining inward, 

 and (2) an angular plate (a) of either cast or wrought iron, witli 

 projecting ribs (/') extending from front to back on its under- 

 side, either cast with or riveted to the same, presenting a con- 

 siderable area, and serving the double purpose of supporting the 

 additional part on the existing grate, and of providing the 

 heating-surface produced by the copper plate and frill-work in 

 my first arrangement. In using iron instead of copper it is 

 necessary however to increase the thickness of these plates and 

 ribs in the inverse ratio of the conductivity of the two metals, 

 or as regards the back plate, from J inch to | inch. 



The arrangement will be rendered more perfect by the use of 

 the bent plate fastened to the lower grate bar, which directs 

 the incoming air upon the heating-surfaces. 



The front edge of the horizontal plate has vandyked openings 

 (it), so as to form a narrow grating, tlu-ough which the small quan- 



tity of ashes that will be produced by combustion of the coke 

 and anthracite in the front part of the grate discharge themselves 

 down the incline towards the back of the hearth, where an 

 open ash-pan may be placed for their reception. 



In adapting the arrangement to new grates, the horizontal 

 grating had better be dispensed with, and the casting with its 

 lower ribs extended downwards, so as to find its fixed support 

 between the back of the fireplace and the inclined deflector plate. 



Mr. Fletcher speaks of the large amount of ashes that would 

 be produced, but this amount can surely not be as great as in 

 the case of a coal fire, seeing that the consumption of solid fuel 

 is reduced to less than one-half, of which nearly one-half is 

 anthracite, a fuel remarkably h'ee from ashes. Neither do I 

 participate in Mr. Fletcher's fear regarding opposition on the 

 part of housemaids, except it be from an apprehension on their 

 part that, with Othello's and the chimney-sweeps', their " occu- 

 pation be gone." 



The tendency of grate-builders of the present day, and also of 



your correspondents, appears to be to look for economy to brick- 

 linings, which no doubt have the effect of producing hot radiating 

 surfaces. I maintain however that such radiation is obtained at 

 too great a cost of fuel, and that superior economical results will, 

 on the contrary, be attained by abstracting the heat from the 

 back of the fire, and concentrating it upon the purely carbonaceous 

 material in front of the same. 



To illustrate my reasoning I may here refer to an experiment 

 which can easily be made of throwing a shovelful of bitu- 

 minous coal into a steel-melting furnace ; the result is an instan- 

 taneous dispersion of the coal, accompanied with a powerful 

 refrigerative action on the furnace. In constructing gas-producers 

 I take advantage of hot walls to turn solid into gaseous fuel, 

 and a fireplace with hot brick bottom and sides is very much in 

 the condition of a good gas-producer, giving out radiant heat 

 no doubt, but combined with rapid distillation of combustible 

 gases into the chimney. This action is made apparent in 

 placing on the fuel towards the back of such a gi'ate when in 

 full glow a piece of wood, which will be seen to dwindle away 

 rapidly without giving rise to flame, the atmosphere immediately 

 over the glowing fuel being essentially a reducing one. 



In my grate the heat, on the contrary, is confined to the coke 

 immediately behind the bars, in contact with the heating gas 

 flames and with the air of the room flowing in towards the 

 chimney, whereas the coke at the back of the grate remains 

 comparatively cool and unconsumed throughout the day. The 

 cold furnace-back also means a cold chimney, and il is rather 

 remarkable to observe that in the case of the application at my 

 office, a thermometer held high up into the chimney showed a 

 temperature of only 130° F., while the front of the grate was in a 

 high state of incandescence. These, I maintain, are conditions 

 most favourable to economy combined with entire absence of 

 smoke or deleterious gases. C.William Siemens 



12, Queen Anne's Gate, S.W., November 24 



CURIOUS IMPRESSIONS IN CAMBRIAN 

 SANDSTONE NEAR LOCH MAREE 

 TN course of the short excursion to Loch Maree and its neigh - 

 bourhood, Mr. Walter Carruthers, of the Inverness Courier, 

 happened, on June 13, to light upon an interesting portion of the 

 Cambrian or Torridon Red Sandstone of the district, forming 

 part of the bed of the burn, near Loch Maree Hotel, on 

 which occur what have been called the Victoria Falls, so 

 named from the fact that the Queen visited them. There 

 an exposed surface of the rock about sixteen feet in length, 

 nearly as much in breadth, and almost perfectly level, is 

 marked by several double grooves quite discernible, and each 

 divided by a very thin raised line. These traverse the whole 

 length of the rock in a perfectly straight line, and on both 

 sides of them are roughnesses which, if we could entertain 

 the idea that the grooving had been caused by some living 

 creatures, might be produced by footprints which have been to 

 a great extent obliterated. The impressions were so striking that 

 they immediately suggested a recollection of the footprints dis- 

 covered in the sandstones of Morayshire and Tarbatness, though 

 there was no other resemblance than their marked character on 

 the broad, flat rock. Having heard that Mr. William Jolly, 

 H.M. Inspector of Schools, was in the neighbourhood, Mr. 

 Can-uthers called his attention to the subject, and indicated where 

 he should find the markings. Mr. Jolly was not slow to examine 

 the spot, and he writes to Mr. Carnithers as follows, as given in 

 the Inverness Courier of July i : — 



"I found your curious lines without difiiculty, guided by your 

 accurate description of their locality. They are assuredly no 

 'mare's nest,' but bona fide ancient impressions of some kind, 

 which should receive the attention of geologists, both on their 

 own account and as existing in the second oldest geological 

 formation in Britain, in which, as yet in Scotland, no evidences 

 whatever of organic Ufe have been discovered. 



"The lines or bands in question occur in the chocolate- 

 coloured Torridon sandstone, the Cambrian of Murchison and 

 Geikie, which is so well developed around Loch Maree, and 

 rises into the great dome of the Slioch, or the Spear Head, that 

 guards its waters. The most distinct of the impressions consists 

 of two continuous flat bands side by side, li to \\ inch broad, 

 and .about a quarter of an inch deep, rmining quite straight across 

 the flat layers of sandstone in silu, and perfectly distinct for 

 sixteen feet, disappearing on the west side under the supermcum- 

 beut rock, and broken only where portions of the sandstone have 



