18*9.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



213 



16 inches long, by 12 inches to 14 inches wide; nailed at top, and 

 fastened by hooks to the slates, which lie immediately beneath 

 them. 



The compound metals used are brass, bronze, and the galvanised 

 iron. No difference exists in the mode of preparing these com- 

 pounds from that observed in England. The bronze is, however, 

 much more often employed than with us. For instance, the 

 columns of the Place Vendome, and of the Bastille; the gates of 

 the Madelaine and St. Vincent de Paul ; the fountains of La Place 

 Louvoise and the numerous statues which adorn all the quarters of 

 Paris are in this metal. 



Painting and Glazing. — The modes of house-painting employed 

 in Paris are similar to those we employ, except that the oils are 

 better, but the colours and white-lead immeasurably worse. In- 

 deed, there is not the same necessity for excellence in the painter's 

 art, so far at least as mere flat tints and common graining are con- 

 cerned, in a country where oak is so universally employed for 

 joinery. For all objects of luxury, however, we are frightfully 

 behind our neighbours. The decorations of Noti-e Dame de Lo- 

 rette, the Madelaine, the former Chamber of Peers, the Louvre, 

 and the Sainte Chapelle, cease to be mere decorations, to pass into 

 the higher walks of art. St. Vincent de Paul, St. Germain 

 I'Auxerois, offer illustrations of polychromic decoration, which 

 contrast painfully with the attempts we see in London. 



These two last-mentioned churches may also be cited as speci- 

 mens of the excellence our neighbours have attained in the art of 

 painting on glass. For drawing and colouring, the windows of St. 

 Vincent de Paul are superior to anything, either ancient or 

 modern, it has ever been my fortune to examine. 



The decorations, painting, and glazing of the cafes and shops 

 might afford useful lessons to the architectural student. Great at- 

 tention is shown to the distribution of the light, and the general 

 tone of the colouring, so as to suit the goods exposed. Glass is 

 cheaper than in England, and in consequence is more prodigally 

 used. The window glass is, however, bad, both in colour and in 

 its powers of resistance; it is thin, green, and wavy. 



Although the above notice of the building materials employed 

 in Paris, &c., has grown to a very great length, I have been forced 

 to pass over some of the most important and interesting subjects 

 the review suggests. The chemical process, called by the work- 

 men saltpetring, and its action upon stones when laid bedwise, or 

 against the bed; the manner in which stones are affected when ex- 

 posed to the various strains; the composition of mortars and ce- 

 ments, and all the phenomena which attend their use in the air, or 

 under water — salt or fresh ; the qualities of woods and metals — 

 have all glided before us; but from the limited time we can here 

 devote to them, these subjects have not met with the attention 

 they merit. Indeed, this remark holds good not only here but 

 elsewhere. Very little is known, comparatively speaking, of the 

 chemistry of our profession; what little we do know may princi- 

 pally be sought for amongst the French authors. Perhaps I may 

 not have occupied your attention in vain, if my remarks should 

 call attention to subjects so full of interest to us, but at present 

 so involved in obscurity. 



DISCHARGE OF WATER FROM RESERVOIRS. 



The Theory of the Contraction of the Movement of Water flowing 

 from Apertures in thin plates, in a Reservoir in which the Surface 

 of the Water is maintained at a constant altitude. By J. Bayer, 

 Lieutenant. (Translated from Crelle's '■Journal fiir die Bau- 

 kunst.' Baud 25.) 



1. 



When an aperture is made in a reservoir of water, the perpen- 

 dicular distance of the upper surface of the fluid from the orifice 

 is in general termed the altitude of pressure. Horizontal aper- 

 tures are distinguished from those which are vertical. The former 

 are made in the horizontal bottom of the reservoir, and at every 

 point have the same altitude of pressure. The vertical orifice is 

 made in the vertical side of the reservoir, and at every point in its 

 vertical section has a different altitude of pressure. This altitude 

 is distinguished according as it is taken at the upper edge, the 

 centre, or the lower edge of the reservoir. The velocity V of 

 water flowing under the altitude H, is the same as that which 

 a falling body acquires in descending the same distance, and 

 therefore V- = 4.(?H, where g is the distance fallen through in one 

 second of time. This equation, called the Torricellian law, was 



first confirmed by the experiments of Michelotti, and neglects the 

 resistance of air. 



The section of the issuing column of water is smaller after it 

 has left the orifice, than at the orifice itself. This phenomenon is 

 termed the Contraction. If, therefore, Q signify the quantity of 

 water which issues in a second of time, and a the section of the 



orifice, and C be put = — , C is smaller than V. Let, therefore, 



C = /cV; it follows that Q = a>lc\ = tak VC+ifH). When Q, a, and 

 H are found by observation, the constant /c, which is called the co- 

 efficient of contraction, may be determined from this equation. 

 Such experimental inquiries respecting the value of k have been 

 very numerous; but they all fail to give a sufficient explanation of 

 the phenomena of contraction; and it is tliis which will be at- 

 tempted in the following pages. 



From the middle of the 17th century, when Torricelli (I6t4) 

 first determined the above relation — namely, that the velocity of 

 the issuing water is as the square of the altitude of pressure — the 

 learned have been much occupied with this subject of Contraction. 

 In the beginning of the last century, the experiments of Poleni 

 directed attention to the discharge which takes place under similar 

 circumstances, from cylindrical and conical discharge-pipes; and 

 endeavours have likewise been made to estimate the diameter of 

 the contracted column. Poleni himself gives it = 4i **f t'^^ dia- 

 meter of the orifice. Newton, by actual measurement, found it 



= 45- Daniel Bernouilli made it by his experiments = — ; and 



Bordu estimates it by direct admeasurement to be = 0'802. In 

 later times, Bossut, Langsdorf, Vince, Michelotti, Dubuat, Eytel- 

 wein, Hachette, Bidone, Smeaton, Brindley, Christian, Poncelet, 

 Lesbros, &c., have made experiments on the discharge of water. 



Bidone, Rudberg, and Navier, have attempted, on different hy- 

 potheses, a theory of the contracted issue of the stream of water 

 through circular orifices. Their hypotheses do not always hold 

 good, and their results do not sufficiently agree with experiment. 



When water issues from an orifice in the vertical side of a re- 

 servoir, it is observed that the particles of water in every part of 

 the reservoir — that is, to the right or left, above or below, the ori- 

 fice — move to the orifice with increasing velocity. Upon this ob- 

 servation the following hypothesis is founded : That the velocities of 

 the particles of water in the reservoir are inversely proportional to the 

 square of their distance from the centre of the orifice. 



If, by help of this hypothesis, all the results observed in the 

 discharge of water be completely explained, so as to be capable of 

 computation, the hypothesis itself must be deemed true. 



From this hypothesis, li e and e' be the distances of two particles 

 of water from the centre of the opening, and v, v their velocities 

 respectively, we have the proportion 



(A) e- : e" = v' : v. 

 For e = e', v will equal v; that is, at equal distances from the cen- 

 tre of the opening the particles of water have the same velocities. 



Let there be described within the reservoir a hemisphere with 

 radius e from the centre of the orifice : all the particles in the 

 surface of this hemisphere will have equal velocities 



FiL.. I. 



Fif. 2. 



To render this observation 'clearer, it may be illustrated by a 

 figure. Let AB, fig. 1, be the projection of the vertical side of a 

 reservoir on the horizontal plane of the paper, which intersects the 

 centre c of ab the aperture; ab the horizontal diameter, and Fm 

 the horizontal axis, of the aperture. In order that nothing may 

 impede the free motion, it will be assumed that the edge of the 



32* 



