3.36 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[September, 



The value of the co-efficient a should be fixed with reference to 

 the construction of the dum, and to the nature of the pool above the 

 dam. 



When a dam serves as a waste-weir, and the pool above the dam, 

 forms proportionally an extensive sheet of water with no current, 

 then the value of a is found, according to Du Buat and Eytel- 

 wein, to be - - - - . - . . ;= 5.70 



For a dam in a small stream, with no wing-walls and em- 

 bankments confining the current, we may put CX - : 



For a dam in a large river, with wing-walls and high em- 

 bankments, leading the current fairly to the fall, we may 

 put a ; 



EX.\MPLE 2. 



A river is 500 feet wide, its average depth in time of a freshet is 

 ten feet, and its discharge at the same time 25000 cubic feet per 

 second. A dam of 500 feet long, and 7 feet high, has been constructed 

 across the river. How much will llie water be raised above its former 

 level, or how much is the height of the fall from the upper level to 

 the lower level ? 



The co-ethcient Ct be here =r 7.5. 



By applying the fornmla VIII, and substituting the above data, we 

 have 



25000' C 25000 \« 



7.00 



7.50 



TT 



~ 7.5- X 500^ 

 Let us assume H = 



H = 



(SH + IO— 7|^ 



; 2.00 ; then we get 



0.0155 



0.0155 



4 4.44 



(iX2-f3) 



18.775 



((H + iO)x5O0J 

 25000 1 « 



t 250 



iTsx 



H = . 



500 i 

 0.0155x17.361 



44.44 



ov H = 2.3G7 — 0.2G9 = 2.098 feet. 



which result is near enough to the assumed value of If, and therefore 

 sufficiently correct. 



Example 3 

 A dam of 800 feet long, and feet high, is to be constructed across 

 a river of about the same width, and which in time of a high freshet 

 discharges 00,000 cubic feet per second, and has an average depth of 

 16 feet. What will be the height of the fall, or the value of H if we 

 put a = 7.5 ? 



Let us assume the value of H ;= 0.8, then we have 



6000' _ _ r 60000 1 » 



lie.sxsooJ 



60000 ) '' 



oc =^ 



7.5»x 800' (Sx 0.8-)- 16— 6) ' 

 100 



•0.0155 



or H == . 



•0.0155 



(. 



\ 13400 

 -0.0155x19.927 



(0.533-I-10)' 



— ^QO 



~ 110.944 ~ 

 or H = 0.901 — 0.30S8 = 0.593 feet. 

 This result does not agree with the value assumed for H, and is too 

 small. From the nature of the formula it follows, that we must as- 

 sume a smaller quantity for H. Let us therefore put H "" 0.6, and 



60000- 



we have 



H: 



0.0155 



" 7.5'x800" (8x0.6-1- 10)'' 

 100 



100 



■0.0155x4.158-' 



I 60000 \' 

 \ 6 8 00) 



60000 \ g 



13280") 



orH: 



108.16 



ov H = 0.924 — 0.316 = 0.608 feet. 

 This result agrees well with the assumed value of H, and is there- 

 fore sufficiently correct. 



ON GEOLOGY, APPLIED TO ARCHITECTURE. 



Being part of a Course of Six Lectures, by G. F. Richardson, Esq., 

 of the British Museum. Ddicered at the' Royal Institute of British 

 Architects. Lecture the Fifth. 



In my last discourse I alluded to the fact that as stones are selected 

 for proximity rather tlian for value, because they are nearest rather 

 than because they are the best, it followed that those countries would 

 naturally exhibit the best specimens of architecture whose geological 

 formations were best adapted for this object, wliose limestones were 

 finest and most abundant, whose marbles were purest and most fre- 

 quently to be found. I reminded yovi that the lovely land of Greece 

 was most favoured in this particular, and that her mountains of lime- 



stone and of marble offered the most picturesque sites for the display 

 of the builder's art, while they contained within their caves and 

 quarries materials of the most valuable and most enduring quality, 

 while the dryness and serenity of the climate of those regions allowed 

 such materials to be placed in situations which our less genial atmos- 

 phere forbids us to expose in the same manner. Yet the geological 

 features of our island are so striking and important, that the geologists 

 of the continent are always anxious to investigate our strata, and tlieir 

 singular organic remains, our Wealden and lias with their colossal 

 ilragon forms, our coal and our primary rocks in the north of England 

 and in Wales ; wliile I have the authority of our friend Mr. Donaldson 

 for the fact that foreign architects who visit this coimtry are alike 

 impressed with the variety and value of the stones which our strata 

 present. The fact is, that our island (-ontains in a limited space, an 

 epitome of, with one or two comparatively unimportant exceptions 

 (the Muschel Kalk is one, the Calcaire Grossiere a second, and the 

 Miocene deposits of the Tertiary series a third), with these relatively 

 insignifi.cant deficiencies our island contains a miniature resemblance 

 of the whole earth. Professor Whewell, the late president of the 

 Geological Society, in his farewell address on quitting the chair, em- 

 ployed in allusion to this fact, and more particularly with reference 

 to the labours and discoveries of my distinguished friend Mr. Murchi- 

 son, an image which is so rare, so ingenious, and so natural, that I can 

 discover no illustration more fitted to convey a correct idea of this 

 interesting fact. AUudirjg to the number and variety of the rocks 

 contained in the limited area of om' own island, and refering in parti- 

 cular to those which had been investigated by the labours of Mr. Mur- 

 chison, he observed that nature in this respect seems to have conde- 

 scended to imitate our own process, and as in the construction of our 

 geological maps we place in the corner minute delineations to serve as 

 types of the strata, so she had placed in our island, our corner of the 

 globe, types of strata whose representatives were to be found elsewhere, 

 diffused only over vast areas, in short, over the map of our planet. Our 

 island exhibits in fact, with the few exceptions I have named, a com- 

 plete ascending or descending scale of the chronology of the earth, and 

 the geological map before you, extending in a direction from south-west 

 to north-east exhibits the regular succession of the strata, either com- 

 mencing with the primary and oldest formations in the north and west 

 of our island, and proceeding down to the tertiary or most modern in 

 the south, or on the contrary, ascending from the modern tertiary in 

 the south, to the older or primary in the north and west. The three 

 grand divisions imder which the strata of our island may be classed 

 are, first, the primary and mountainous or mining districts, whose in- 

 habitants of course are miners and mountaineers ; secondly, the mid- 

 land regions exhibiting a succession of fertile hills and valleys over- 

 spread with towns and cities, and crowded with a dense population, 

 whose industry is supplied by the coal with which the strata of these 

 districts are abundantly interspersed. The third class is formed by 

 the chalk and oolitic limestones which extend from the western to the 

 northern coasts of our island. To pursue these routes along tlie map, 

 the traveller who would wish to investigate the first of those geolo- 

 gical series which we have described, would be required to start from 

 the extremity of England, the Land's End, to traverse the whole of 

 Cornwall and the north of Devon, and thence passing through Cumber- 

 land by the Isle of Man, to the south-western shores of Scotland, 

 should proceed either through the. hilly districts of the border coun- 

 ties, or along the Grampians to the German Ocean. Such a traveller 

 would meet in all his journey little else than mountains and mines, 

 and would consider the countiy he had traversed barren, and cold, and 

 thinly peopled, its scanty population being composed of miners and 

 mountaineers. To take the second route a traveller would start nearer, 

 from the coast of Devon, and crossing the Midland Counties from the 

 mouth of the Exe to that of the Tyne, would find a succession of fertile 

 and highly cultivated scenes, interspersed with numerous towns and 

 cities, and in many parts crowded with a manufacturing population, 

 who derive the chief supply and incentive to their industry from the 

 vast mines of coal with which these districts are abundantly supplied, 

 they being located in the new red sandstone. The largest, most con- 

 siderable, and most infiuential towns in England are placed in this 

 peculiar stratum the new red sandstone, as the following list will 

 evince: Exeter, Bristol, Worcester, Warwick, Birmingham, Lichfield, 

 Coventry, Leicester, Nottingham, Derby, Stafford, Shrewsbury, Ches- 

 ter, Liverpool, Warrington, Manchester, Preston, York and Carlisle. 



The third route would extend nearer from the coast of Dorset to that 

 of Yorkshire, from Weymouth to Scarbro', and the traveller through 

 such a district would pass only over elevated plains of oolite limestone 

 and chalk, without a single mountain, or mine, or coalpit, or a manu- 

 factory of any importance, and woukl meet with a population almost 

 exclusively agricultural. These different appearances being deducible 

 from stratification. 



