242 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[August, 



tunatelv, not occasion for many windows, — very luckily for none just 

 immeJiately adjoining the portico, wliere any apertures of tlie kind 

 would have cut up the mass from which it projects ; still it was ne- 

 cessary to obtain several windows, and those immediately over each 

 other, for rooms on four different floors. To combine so many distinct 

 apertures into a single architectural composition that would accord 

 with all the rest of the portico was no small ditTieulty, yet the problem 

 lias been so happily solved that those two features produce the effect 

 of inner loggias with a smaller order, and instead of there being scat- 

 tered spots and patches, there are what are adequate to deep masses 

 of shadow. Even taken as an example of a Venetian window set 

 within an arcade, the composition is marked both by oiiginality and 

 good taste. It even exceeds two squares in height, and therefore has 

 adignifiedairofloftiness,and of compactness as toculumniation,thevery 

 reverse of the meagre and sprawling appearance which is soolfensive 

 in many windows of the kind. We take it for granted that our readers 

 are aware that there are no more than two of these windows within 

 the portico of the Exchange, viz., one on each side of the central re- 

 cess in which the entrance is placed, and that each of them fills up a 

 compartment answering to two intercolumns and an intervening co- 

 lumn of the external elevation, in other words, that the pilasters, whose 

 edges are indicated in the cut, answer to the first and third column of 

 the portico from either end. The entire width within the clear of the 

 pilasters is 20 feet, consequently the scale of the cut is as nearly as 

 may be one inch and ^ to ten feet, from which the other measure- 

 ments may be ascertained without difficulty. 



ON THE RESISTANCE REQUIRED TO SUSTAIN BANKS 

 OF EARTH OR OTHER MATERIALS. 



Being an distract of Papers read before the Royal Irish Academy and 

 the InsiitiUion of Civil Engineers, Ireland, 



By John Neville, C.E., Dundalk. 



A B D is any bank with a vertical or inclined face A B, and a hori- 



zontal or inclined top B D, then if A D be the position of the plane of 

 repose, the horizontal resistance required to sustain a fractured wedge 

 A B C is equal to 



A B C X tan D A C (1.) 



and the position of A C when this resistance is a maximum is deter- 

 mined as follows: — 



Through A draw A O parallel to B D. Draw any line E O cutting 

 A D at right angles ; on E O describe a semicircle, and from G, where 

 the circumference cuts the plane of repose, as distance, with O as 

 centre, describe an arc cutting E O in F, join A F and produce it to 

 C, then the resistance required to support F D C is a maximum. 

 Also, let fall A H perpendicular on B D produced. Put A H = A, 

 BAH= 6, DAH;=c, and W = the weight of a cubical unit of the 

 bank. Then 



R: 



i'W/sec C — 1/ tan 6 tan c + 1 ' 



•2 \ 



A'W 



(2.) 



R = ^ — '-^ (V tan c + cot c — V^n 6 cot c)' (2'.) 



For the particular case where B D is horizontal the equation 



(25) R=-^ (tan!+tanc+— .-2(tanctan!+*-?^^^+^+l)^\ 

 ^ 2 tan ! \, tan z tan j ' ' J 



is given by Tredgold in the Article Masonry, Encyclopedia Brittanica, 

 7th Edition, where i is the complement of the angle of repose, 0=6 

 in equation (2) or (2'), and S ^ W. Now this equation (25) is 

 t an c + 1 

 tan i 



Incorrect, as the term 



under the vinculum should be 



of equation (2'), which is general whether the top is horizontal or in- 

 clined, and is easily calculated from. 



The first table is given by Tredgold as calculated from equation (25) 

 in the work referred to, and the second is calculated from equation (2) 

 or (2') to the same data, where the values in the last column are about 

 double those determined by Tredgold. The other difterences are im- 

 material. 



tan c tan i A- \ . ... ,, ,. . , ,, , 



:— ^ — , 111 which case the equation is merely the development 



The general geometrical constructions render — from equation (1) — 

 the calculation of R easy for any particular case. When A B is at 

 right angles to B D, it is easy to show that A C bisects the angle 

 BAD, hence the equation of Prony holds good nhen A B iS perpendicular 

 to B D, whether A B is vertical or inclined. 



Equation (2) or (2') gives the resistance required for dwarf walls 

 at the toes of cuttings or embankments. 



It was shown that however the top B D may slope up to the angle 

 of repose, that the resistance for the same height of wall when B D is 

 horizontal could not exceed the ratio of 4 to 1 whatever the angle of 

 repose and height of the embankment may be, and that in slopes of 

 repose of IJ to 1 the ratio of the resistances could not exceed 7 to 3 

 for dwarf walls. 



EVAPORATIVE POWER OF DIFFERENT KINDS OF COAL • 



AND THEIR RELATIVE VALUES. 



Experiments made wider the authority of the Js'avy Department of the 

 Untied States, 



An Act of the American Congress, approved Sep. 11, 1841, author- 

 ized the making experiments upon the properties and relative values 

 of diHeient kinds of coal. In virtue of this authority. Prof. Johnson 

 of Philadelphia commenced an investigation on which he has long 

 been zealously engaged : the result of his labours is communicated in 

 a large volume ordered to be printed for the use of the Senate.* This 

 volume is in large octavo, and contains upwards of GOO pages of closely 

 printed matter; it would therefore be quite impossible to make a 

 faithful abstract of its whole contents, but it is confidently hoped that 

 the following extracts, giving some account of the manner in which 

 the experiments were conducted, and detailing a portion of the ulti- 

 mate results, will form a valuable and acceptable paper. 



The experiments have been conducted by Prof. Johnson with the 

 greatest skill and care. To his qualifications as an experimenter he 

 has added the knowledge of mathematical philosophy and the few 

 mathematical notes which occur in his report appear quite satisfactory 

 and add to the reader's confidence in his c.ilculations. His report is 

 beyond doubt one of the most valuable contributions which have been 

 made in modern times to practical science. We have given the results 

 arrived at respecting part only of the coals experimented upon. Each 

 of the numerous samples was made the subject of several experiments 

 from which general averages have been deduced. Of all the nume- 

 rous tables which accompany the volume, we have been able to give 

 the last only, which exhibits the results ultimately arrived at ; and of 

 this table w.e transcribe that part only which refers to the British and 

 the principal American coals. 



Extracts from the Report. 

 Object of the Inquiry, 

 The inquiry, now nearly completed, was instituted primarily en 

 account of the difficulty which had been experienced, and the com- 

 plaints which had been made, relative to the qualities of the coals 

 procured for the naval service. It had been found that articles fur- 



ITie number of copies ordered to be printed was 11,000. 



