106 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



f April, 



Port Clarence on the river Tees, where several of them have been 

 in use for some years, and are verj' effertive. 



The ten drops erected on tlie west side of the iVIiddleshro' Dock 

 are almost similar, in every respect, to tliose at I'ort Clarence. 

 The priticiple of their construction and mode of operation will be 

 readily understood by a reference to the enpravinps, Plate yH- 

 Fijr. i sliows a front elevation, and fig. 2 a side elevation of the 

 drop and its machinery ; fig. 3 sluiws the machinery, «ith the 

 cradle and wagon, drawn to a larger scale ; the same letters refer 

 to the same parts in the different drawings. 



The wagon A, weighing about 30 cwt., and containing one chal- 

 dron or 53 cwt. of coal, is shown standing on the moveable stage 

 or cradle B, which is suspended by means of chains passing over 

 the sheaves C, C ; the ends of the chains are attached to the large 

 sheaves F, F, the latter being cast with grooves of unequal depth, 

 to acc<mnnodate the two chains, which it will be seen are of un- 

 equal length, aiul reciuire a corresponding inequality in the sheaves, 

 to preserve tlie cradle in a horizontal position. These sheaves are 

 fixed on a strong iron axle H, on the extremities of which are two 

 other sheaves or puUeys K, K, to take the chains which sustain 

 the counterbalance weights M, M. The break machinery for 

 lowering the wagons consists of the toothed wheel P, 7 feet 

 diameter, fixed on the same axle II ; the pinion-wheel Q, 2 feet 

 diameter ; and the break-wheel R, 6 feet diameter, having a break 

 over its whole circumference, worked by a strong lever-handle, 

 which controls the descent of the loaded wagon, and its ascent 

 when emjity. 



When tlie machinery is at work, the loaded wagon is run on to 

 the cradle, or stage, B, and is stopped by wooden chocks in its 

 jroper position, directly over the liatchway of the vessel to be 

 oaded (T, T, fig. 1.) Tliebreaksman then releases the break- wheel, 

 when the cradle and wagon descend perjiendicularly, the susjiend- 

 ing chains winding off the slieaves F, F, the counterbalance 

 weights rise, and tlieir suspending chains wind on to the sheaves 

 or pulleys K, K. The cradle, with the wagon upon it, still main- 

 taining its horizontal position, having nearly reached the ship s 

 deck, tlie contents are discharged by a man who descends with it 

 for that purpose ; the counterbalance weights then have the pre- 

 ponderance and the operation is reversed, by the weights descend- 

 ing and the empty wagon and cradle rising to their original posi- 

 tion. The wliole is so guided and controlled by the breaksman, 

 and the counterpoise weight so adjusted, tliat the wagon can be 

 made to descend and ascend quickly or slowly, or be stopped with 

 ease in any position, either ascending or descending. 



The drops at Middlesbro' Dock are constructed of strong wooden 

 framework fixed on Memel fir piles, and the cost of the ten drops 

 was £7,300, or £730 each, including all the timber, iron-work, ma- 

 chinery, and the labour in fixing. 



Eacli of these drops can ship a wagon load of 53 cwt. in a 

 minute, or about 150 tons in an hour; but as the coals cannot be 

 trimmed off so quickly in the ship's hold, about thirty wagons an 

 hour may be taken as the ordinary rate of working. Forty 

 wagons, containing a chaldron each, which are = 5 keels or 106 

 tons an hour, may be considered the limit of working. 



In the year ending 1st July, 1845, 505, 186 tons were shipped by 

 means of the ten drops here described. The shipment in the six 

 months ending 31st December, 1845, amounted to 264,180 tons. 



Ic 



ON THE RESISTANCE TO BODIES IN FLUIDS. 



On tlie relation between the Velocity and the Reni.itanre en- 

 ixuntered hyhiidies moving in Fluids. By John Mortimku Heppel, 

 Grad. Inst. C.E. — (Read at the Institution of Civil Engineers.) 



The determination of the relation between the velocity and the 

 resistance encountered by bodies moving in fluids, has always been 

 an interesting topic of iniiuiry, as well to the speculative philoso- 

 pher as to tlie practical mechanist, and perhaps im no portion of 

 physical science have more pains been spent ; wliether looking to 

 the sagacity with whicli experiments have been devised, the libe- 

 rality witli which tliey have been carried out, or the mathematical 

 acumen wltli which tlieir i-esults have been classified and brought 

 under gener.il laws. To enumerate the names only of the men, 

 illustrious )py tlieir science, who have brouglit tlieir energies to 

 bear on tliis suliject, would fill a larger space than those few re- 

 marks are intended to occupy. It is sufficient to mention Newton, 

 who in this, as in so many other departments of philosophy, first 

 shed the light of his brilliant genius on the former obscurity ; — 

 after him the scarcely less celebrated Daniel Bernouilli, and in 



latter times Bossut and De Buat, whose patience and accurate re- 

 search opened such a multitude of observed facts to the contemp- 

 lation of the theorist. Again, the valuable experiments of the 

 French Academicians ; the indefatigable labours of tlie late 

 Colonel Beaufoy, so liberally made available for the objects of 

 science by liis son ; and lastly, though not among the least, must 

 be mentioned tlie excellent experiments on canal boats by Palmer 

 and Macneill, given in the Transactions of the Institution (vol. I. 

 pp. 165-237). After such a retrospect it may appear presump- 

 tuous in a young and unknown individual, attemjiting to add 

 anything to a subject already enriched by such contributors; as 

 his remarks, however, are brought in an Iiumble and modest spirit, 

 and so far as he is aware, have not been anticipated by any pre- 

 cisely similar, he begs to lay them, without further introduction, 

 before the Institution. 



It will no doubt be recollected, that in the cases already glanced 

 at, the almost invariable method of experimenting has been to 

 attach a weight, or other known moti\'e force, to the body in ques- 

 tion, and to determine, by direct observation, the quantity of this, 

 corresponding to an uniform velocity of progression. From this 

 method it has necessarily followed, in most instances, that the 

 bodies subjected to experiment were of moderate dimensions, and 

 the theoretical views derived from the observations, have been ex- 

 tended to those which from their magnitude have been placed 

 beyond the range of direct experiment. In the experiments of 

 Palmer and ISIacneill, the same mode of proceeding was adopted, 

 by applying the dynamometer to boats moving on canals, and from 

 the magnitude of the scale of these experiments, as well as from 

 the care and accuracy with which they appear to have been con- 

 ducted, they must be very valuable. Gigantic, however, as these 

 bodies were, as compared with those which had previously been 

 brought under investigation, they become dwarfs in respect of the 

 vessels, the knowledge of whose properties is every day becoming 

 a matter of deeper practical importance. It has often surprised 

 the author, that these vessels themselves had not been made the 

 object of experiments, with reference to this question, and more 

 especially, if it can be shown, as is here attempted, that those pro- 

 pelled by steam, more especially, unite all the conditions requisite 

 for obtaining easily and simply, accurate and important results. 

 The form, however, of these experiments, must differ from that of 

 former ones, as the tractive power requisite to maintain a high ve- 

 locity, in such large bodies, would be far greater than could be 

 conveniently disposed for such a purpose. 



There is, however, another no less certain mode of inferring the 

 amount of resistance encountered by a body, which is, to remark 

 the diminution of velocity produced in a given small portion of 

 time, when the body is exposed to the action of tliis resistance 

 alone, from which diminution of velocity, the force which produced 

 it may be inferred ^vith mathematical precision. Let it be pre- 

 sumed, in the first instance, that the velocity with whicli the vessel 

 is at any instant moving through the water, is capable of being 

 measured and observed ; then having set the vessel in motion, 

 with a given \elocity, let the action of the motive power be 

 stopped. The only forces to whose action it will then be exposed, 

 are the resistance of the water and the air, of which the former 

 will be by far the more considerable ; but of both of which it will 

 always, under ordinary circumstances, at the same velocity, have 

 the same amount to encounter, and whose amount therefore con- 

 stitutes the obstacle to be overcome by the motive power, and de- 

 termines the quantity of that power always required to maintain 

 that velocity. From the instant when the engines are stopped, 

 the speed of the vesssel will obviously diminish, and let the amount 

 of its diminution during some small interval of time, say a second, 

 be noted ; that is to say, the difference between the velocity at the 

 commencement and at the end of that interval. Nov,' if the 

 vessel had been subjected to the action of a force equal to its 

 whole weight, the amount of velocity destroyed in a second would 

 have been 32 feet per second, therefore, as 32 feet is to the observed 

 loss of velocity in feet per second, so is the whole weight of the 

 vessel, as shown by its displacement, to the force by which this 

 loss of velocity has been produced ; that is, to the united resist- 

 ance of the water and the air, corresponding to the velocity in 

 question. It is Iiere assumed, that the force of resistance, for the 

 small period of the observation, maybe regarded as uniform; a 

 supposition which is not precisely true, as the resistance diminishes 

 with the velocity ; the smaller, however, the interval of time which 

 is taken, the nearer will this supposition be to the truth, and if tlie 

 infen-ed resistance be taken to correspond neither to the initial 

 nor the final velocities, but to their mean, the error will become 

 infinitesimal. A more important source of error would be found 

 ia the circumstance of the resistance of the paddles, or the screw. 



