424 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[NoVKMBKft, 



tion, to eiicli liundreil ]Jcun(ls uf Imlin-nibber. of half an ounce of corrosive 

 sublimale. or other mctalhc salt which will resist vegetable decomposition. 



These mixtures are also iiilcnilcd lo be used in ship-building instead of felt, 

 between tlie copper and plankin;.; of the ship ; being made in thin sheels_ 

 which are cemented in their places, and then coated on ihe outside with ce- 

 ment, and before this ln^comcs dry, Ihe copper is fixed on in ihc usual man- 

 ner. They are also made into blocks or masses of suitable forms, and applied 

 to the purpose of filling the spaces between the limbers or plankinR of ships ; 

 being cemented to the wood, and to each other, so that the w hole becomes 

 impervious to water. For boat-building, the mixtures are formed into sheets, 

 planks, or slabs, and used with or without timber courses. 



A substitute for tluor-cloth is formed, by rolling the material into large 

 thin sheets, the sides ol which are cut | arallel,and be vi lied oil to thin edges ; 

 these edges are rubbed over with India-rubber cement, and united by causing 

 them to overlap, and then pressing them carefully together ; when tlic ce- 

 ment is dry, the side that is not intended to be printed upon is coated with 

 cement, and a piece of canvass, cloth, or other woven fabrics applied thereto ; 

 the substitute for floor-cloth, thus made, is now ready to be printed on. 



For covering roofs, walls, or other surfaces, wdiere it is rerpiired to exclude 

 rain and moisture, the material is rolled into sheets, which are cemented to 

 the surfaces lo be covered, and to each other. 



For paving or covering Iloorsor roadways, the sheets or slabs are cemented 

 lo the " subsurface," and to each other. 



The patentee says, in conclusion, — " I hereby declare that I lay no claim 

 to the invention of any of the mi.\tures herein referred to, nor to the method 

 of preparing them ; such mixtures, and the processes of preparation, being 

 already well known. But what I claim, as my invention, is, their application 

 to the purposes herein described, in the manner 1 have pointed out ; more 

 particularly the cementing the said mixtures to some other body, and to each 

 other, according to the respective purposes to which they are to be applied." 



MR. DENTON'S "A" LEVEL. 



The annexed 

 woodcut shows 

 the instrument 

 — its figure will 

 explain the rea- 

 son of its being 

 called the " A 

 Level ;" while 

 the observer 

 will compre- 

 hend at a glance 

 its portability 

 and the facility 

 with which it 

 may be used 

 either on the 

 surfar^e or in the 



trench. The b ir B turning up on a hinge and falling into grooves cut 

 in the legs A, these legs may be closed, as a pair of compasses fold ; 

 and the whole may be used as a rod for measurement. The legs A 

 are sufficiently narrow to stand in the narrowest trencli; while the 

 false feet F aftord the means of stationing the instrument on the 

 surface. 



The object of the instrument is to assist foremen and workmen in 

 testing and preserving an uniform fall in all works requiring such regu- 

 larity. A spirit level, if understood by workmen, is a thing easily 

 put out of order, and is at all limes liable to be broken; its use, there- 

 lore, is dreaded by workmen, as a process involving too much time, 

 rare, and precision, for their fingers to perform. 



In drainii'g and sewering, if the first object of the operator is lo 

 direct his drains according to the best fall of the ground, the next 

 point of importance is that the floor of the trench, and the course of 

 the tiles, soles, or bricks should be even and regular from the top to 

 the bottom of the drain. Any hollow in the drain intercepts the sedi- 

 mentary matter which the How of the drain water would otherwise 

 cairy out with it; the sectional area of the water-way is thereby les- 

 sened, and llie sediment, gradually accumulating, after a time causes a 

 stoppage, the drain bursts, and the work has to be re-done. 



'J'iie levrl placed in the trench, as it is dug preparatory to laying in 

 the tiles, ludirales by the plumb-line any irregularity bad work may 

 occasion. Such use of the instrument is merely analogous to the mode 

 by which the carpenter applies his square and plummet. It is my 



wish to prove lliat the extended principle upon which the A level is 

 based is so sound, that if accurately constructed, the instrument can- 

 not work otherwise than with perfect efficiency, in determining the 

 average fall of surf ace btlnetn any two spots within night of each other. 



It should be observed, that the legs of the instrument being equal 

 in length, form, with the base upon which they are placed, an isosceles 

 triangle, and that, when that base is perfectly level the plumb-bob 

 pendent from the apex must necessarily divide the triangle directly in 

 half. This admitted, it is equally clear that by means of a bar con- 

 uecling the two legs at any given distance, and exhibiting on its face 

 the centre or half of the angle at Ihe apex, any person is competent, 

 guided by the plumb-line, to raise or depress one leg until it stands 

 on a level with the other: the plumb-line will then liit the centre. 



Now, as the plummet will always hang vertically, by reason of its 

 weiglit, any rise or depression of either leg is immediately indicated 

 on the connecting bar by the equivalent deviation of the plumb-line 

 from the centre. 



The angle A 

 Ii C is equal to 

 the angle D E F, 

 /. e., the angle 

 made by Ihe 

 hypolhenuse or 

 surface with the 

 horizontal line, 

 is ecpial to the 

 angle of the line 

 dividing the tri- 

 angle in half, 

 with the vertical 

 line. 



Thus, the difterence of height between D and E may be calculated 

 by multiplying the natural sine of the angle D E F (read off on the 

 bar as A B C, if the index represents degrees), by the length of the 

 ground spanned between E and D. In the A Level, this is already 

 done ; and instead of degrees and minutes, inches and quarters are 

 divided on the bar, so that the operator may at once read from it the 

 difterence of height between the two spots upon which the instrument 

 stands, and vice versii. If it is required to sink one leg an inch below 

 the other, the ground is lowered until the plumb-line strikes the 1-inch 

 division of the index on the bar. 



It will be seen, that at a certain distance from tlie apes, on each leg 

 a line of sight is shown. On the one leg there is a sliding sight-hole 

 answering to a fixed index, agreeing with that on the bar B; on the 

 othiT leg, there are cross hairs fixed, the centre of which are exactly 

 the same distance from the apex as the nonius of the index on the op- 

 posite leg. The line of sight therefore from these two points is ever 

 parallel with the base of the instrument. 



To arrive at Ihe average fall of surface from the top to the bottom 

 of a field, the instrument must be placed on a level by means of the 

 plumb-line. The operator must then send forward his assistant-work- 

 man to the spot D, at which he intends to end his drain, with a stick 

 marked by a paper fixed in it at a height C above the ground, agree- 

 ing with the 



height of Ihe — '"^ 



cross hairs B, 

 above the base 

 of the instru- 

 ment. He then 

 slides up or 

 down the sight- 

 hole until he fixes Ihe cross hairs upon Ihe paper in the stick. 



This line of sight, CBC, is parallel with the general line of surface, 

 E D (regardless of its sinuosities), and therefore forms, with horizontal 

 line of sight ABA, an angle C B A, equal to the angle D E F, formed 

 by Ihe datum horizontal and the surface. 



Now, as the opposite angles of lines crossing each other are equal, 

 the angle A B C is equal to the angle C B A ; and we have shown 

 that the angle C B A is equal to the angle D EF; therefore A B C is 

 equal to D E F, and consequently you are enabled to read from the 

 index at C, the angle converted into inches and fpiarlers, which is com- 

 mon to the whole distance from E lo D. The height thus read oft" is 

 transferred to the bar B, and retained by the shifting limb G (see the 

 woodcut), to the edge of which the plummet is aftervi'ards worked. 

 This limb is used only lo save memory, and assist the mm who cannot 

 read. 



From the explanation given, I hope I have shown that, without any 

 measurement of distance wliatever, the average fall of surface is ar 



