WATER. 



When it is intended that the fhip or mill (hould be fta- 

 lionary, it muft be anchored, moored, or otherwife made 

 faft, fo as to fwing with the tide when nccefTary ; but the 

 mill may be worked while the veffel in which it is ereftcd is 

 failing, when wind and other circumilances permit. 



The number and fize of the water-wheels to be ufed may 

 be varied, according to the fize of the fhip or veflel, or to 

 the ftrength of the tide or current, and the power required ; 

 and the wheels may be conftrufted as in common underfhot 

 jnills, or with folding-floats, for the more readily freeing 

 them from the water : two wheels are to be placed vertically, 

 on an horizontal axis, of fuch length, that, the axis being 

 placed acrofs the (hip or veflel, one wheel may run on each 

 fide of it on the fame axis. 



A mill conftruAed in the manner above defcribed may 

 be moved by the ilrength of from two to fix large water- 

 wheels, or fuch other number as the (hip or velfcl will ac- 

 commodate. Thcfe water wheels may dip into the water 

 from three to four, or more feet deep ; they (liould be 

 fo connefted together as to be ealily engaged with and dif- 

 engaged from each other, fo that during the weak part of the 

 tide they may all be made to aft on one pair of mill-ftones, 

 if neceffary ; and as the ftrength of the tide increafes, more 

 ftones or other machinery may be put in motion, fo as at all 

 times to do bufinefs in proportion thereto. 



In a mill of this kind the water-wheels do not admit of 

 having water-courfes, or any equivalent contrivances, to con- 

 duft the water to the wheels, as in other underfhot wheels ; 

 but the float-boards muft be large enough to receive the 

 power required from merely dipping into the current of the 

 tide-water. 



The veffel of the mill in the Thames is the luil! of an 

 old (hip of two or three hundred tons burthen, which being 

 moored in the river by chains, fo that it can fwing round 

 when the tide changes, the wheels will always turn the 

 fame way round ; one water-wheel is fixed on each fide of 

 the veffel, a long iron axis being common to both ; the ex- 

 treme ends of the axis are fupported in a frame w-ork of 

 timber, and another very ftrong frame of timber is fixed 

 outfide of the wheels at the level of the water, wliich floats 

 in the water, and is only attached to the mill by chains ; this 

 is to proteft the wheels iVom injury, by veffels which pafs and 

 repafs. Each water-wheel is i8 feet diameter, and 14 feet 

 broad ; the float-boards are each 3 feet deep, and are about 

 fixtcen in number, affixed on the circumference of cart iron- 

 wheels, or circles, which are i 2 feet diameter, there are three 

 of thefe circles for each wheel ; hence we find each float- 

 board expofes a furface of 42 fquare feet to the aftion of the 

 current, and if we fuppofe each wheel to have two floats in 

 aftion at the fame time, the power of the mill will be derived 

 from 168 fquare feet afted upon by the water, which feldom 

 exceeds a velocity of four miles per hour, or 352 feet per 

 minute. 



The iron axis of the water-wheels is a hollow tube of nine 

 inches diameter outfide, and five inches within, made in four 

 lengths of 12 feet each, properly joined together, and ex- 

 tending acrofs the veffel from one wheel to the other. On 

 the middle of this axis a large wheel of 1 1 feet diameter is 

 fixed, and furrounded by a brake or gripe like that ufed in a 

 wind-mill, the ufe of which is to ftop the mill when it re- 

 quires repairing. Near to this brake-wheel is a large be- 

 villed cog-wheel 1 3 feet diameter, with 89 cogs, which gives 

 motion to a bevilled pinion two feet eight inches diameter, 

 with eighteen cogs fixed on the top of a vertical axis. On 

 this axis is alfo a large horizontal fpur-wheel 12 feet dia- 

 meter, with 201 cogs, which gives motion to pinions of one 

 foot diameter, and 1 7 cogs fixed on the fpindles of the mill- 



9 . 



ftones. There are four pair of mill-ilones, two pair of 

 4-1 feet and two pair of 3^ feet diameter, and the mill alfo 

 works a dreffing-machine for the flour. The mill-ftones 

 make 575 revolutions for one revolution of the water-wheels, 

 which move very (low, fcarcely two turns ^^r minute, in the 

 moft favourable periods of the tide. The circumference of 

 each taken through the middle of the float-boards is 47 feet ; 

 hence the float -boards move about 94 feet per minute, when 

 the mill-ftones make their proper number of revolutions to 

 grind with the greateft effeft. 



It was found that on a flood-tide, this mi'l would drive two 

 pair of 3-5 feet mill-ftones, and a flour drefling-machine, but 

 on the ebb-tide only one pair of 4-feet ftones and the ma- 

 chine ; thus it is only the performance of a fmall mill, al- 

 though the wheels are of large dimenfions, and it would 

 require enormous wheels to make an effective floating mill 

 in the river Thames. 



Tfiis machine is now removed from the river, becaufe it 

 was found to do fo much injury to the veffels which continu- 

 ally ran againft its floating frame, and the repairs of the da- 

 mages frequently done to the mill by ice and the craft took 

 away all the advantages of the mill. 



Lfnili-rjhot IVheeh with oblique Floats. — Attempts have 

 been made to conftruft water-wheels for tide-rivers which 

 receive the impulfe obUquely, like the fails of a common 

 wind-mill. This would in many fituations be a great ad- 

 vantage. A very flow but deep river could in this manner 

 be made to drive mills ; and although much power would 

 be loft by the obliquity of the impulfe, the remainder might 

 be very great. Dr. Robinfon fpeaks of a wheel of this kind 

 which was very powerful ; it was a long cylindrical frame, 

 having a plate ftanding out from it about a foot broad, and 

 furrounding it with a very oblique fpiral like a cork-fcrew. 

 This was immierfed about one-fourth of its diameter (which 

 was nearly 12 feet), having its axis in the direftion of the 

 ftream. By the work which it was performing, it feemed 

 more powerful than a common wheel which occupied the 

 fame breadth of the river. Its length was not lefs than 

 20 feet ; had it been twice as much it would have been nearly 

 redoubled in its power without occupying more of the 

 water-way. It is probable fuch a fpiral continued quite to 

 the axis, and moving in a liollow canal wholly filled by the 

 ftream, might be a very advantageous way of employing a 

 deep and flow current. 



In the Tranfaftions of the Society of Arts, vol. xix. a 

 water-wheel is defcribed, in which the float -boards are placed 

 obliquely to the axis of the water-wheel at about an angle 

 of 40 degrees, being fixed to the rim in pairs, which are 

 inclined equally to the axis of the wheel, but in oppofite 

 direclions to each other ; fo that the two float-boards of 

 each pair point towards each other in an angle of about 

 80 degrees, and if the pair of floats were continued they 

 would meet in the middle of the breadth of the wheel. The 

 water is made to ftrike the floats within this angle, and in 

 confcquence all the water which is emitted by the fluice and 

 ftrikes upon the oblique floats will be reflefted from the fides 

 or ends of the two pair of float-boards towards the vertex 

 of the angle, which they make ; but the pair of floats 

 do not touch each other, fo that the vertex of the angle is 

 open ; but to prevent the water pafling freely through the 

 open angle, one of the float -boards is made to extend far be- 

 yond the vertex, or point, where they would interfeft, and 

 the other is made to fall ihort of it, neverthelefs the water 

 would certainly pafs through the opening. It is ftated, that 

 the motion of the ordinary wheel with parallel floats is 

 greatly retarded by the reliftance which they experience in 

 rifing up or quitting the tail-water of the ftream, from the 



preffure 



