WITHDEAWN FROM THE ACTION OF GRAVITY. 419 



pfmilar to that used for the formation of the laminar catenoid of oil, (§§ 3 and 11.) 

 a system of which I here z'eproduce (fig. fi) the design in perspective, 

 although it has been already given in the plates of the second 

 series ; 2d, a syst(^m of rings of the same kind, but having a di- 

 ameter of only three centimetres ; 3d, a system of disks seven centi- 

 metres in diameter, the lower one of which is borne upon three feet 

 more solid than those of the rings, and issuing from points situated 

 between the border and the centre, while the upper disk is sustained 



by an iron wire fixed perpendicularly at its centre; 4th, a small ^- — i s,^ 



table with adjusting screws ; 5th, several common clay pipes, and C^ y 

 a soft brush of middle size; 6th, a support consisting of a vertical j ""' f 

 rod, along which slides, with little friction, a horizontal arm : it is to / I 



the extremity of this arm that we attach either one of the upper ' » 



rings by the end ?n of the handle of its fork, or the upper disk by the end of the 

 iron wire which sustains it ; for this support I have adopted a cathetoraeter; the 

 ring or the disk is attached, by means of an intermediate piece, to the exti'emity of 

 the eye-glass. We obtain thus, besides the other conditions, the faculty of read- 

 ing on the scale of the instrument the quantity by which the ring or the disk is 

 raised or lowered. 



With a view to give more stability to the lower rings, each of them is fixed 

 by its feet with drops of sealingwax in a small porcelain saucer, and, that ad- 

 hesion may be better secured, the glaze of the porcelain should be previously 

 removed with emery at the places which are to receive the wax. When the 

 rings and disks are new the glyceric liquid adheres imperfectly, and the laminar 

 figures burst while one is trying to form them, or almost immediately after their 

 formation; but this difficulty is removed in the following manner: the apparatus 

 is immersed in nitric acid diluted with four times its volume of water, until the 

 surface of the pieces in question is perceptibly oxidized, which requires not 

 more than a minute ; they should then be carefully washed with pure water, wiped 

 with a strip of filtering paper, and left to dry ; they are thus rendered fit for service 

 indefinitely, and will always yield durable figures. 



Let us obsei-ve now how the experiments are prepared. The cathetometer is 

 to be first rendered quite vertical, and the upper ring or disk attached to it ; if 

 this ring or disk appear to be not exactly horizontal, the position must be cor- 

 rected by cautiously bending with pincers the iron wire which sustains it. The 

 lower piece, whether ring or disk, is then to be placed on the table ia siich 

 manner that it shall be vertically below the other, Avhen, by means of the adjusting 

 screws and by slight displacements of the lower piece, it is easily managed that 

 in lowering the upper one the two rings or disks shall exactly cover one another. 

 Then, after having raised the upper one, we carefully wet each of them with 

 the glyceric liquid. For the lower ring we use, for this purpose, the brush well 

 saturated, and for the upper a capsule containing the same liquid, into which 

 this ring is to be plunged. After the withdrawal of the capsule the ring will 

 be found to be occupied by a plane film, but this we break. As to the disks, 

 the liquid is spread with the brush over the whole of the two opposite faces, and 

 then the liquid contained in the capsule is brought into contact with the moistened 

 face of the upper disk, after which the capsule is removed. We should add 

 that in the case of the rings it is necessary to pour a little water in the saucer 

 which supports the lower one, without which the small portions of glyceric 

 liquid which ftdl therein would attack the sealingwax and eventually detach it 

 from the porcelain. 



§ 15. Let us suppose now that it is the laminar catenoid which is to be realized. 

 We take the system of rings of seven centimetres, and after having made the ar- 

 rangements above indicated, lower the upper ring until it is separated from the 

 other by not more than a fraction of a millimetre ; then let the brush, "well 

 steeped with glyceric liquid, be several times applied along the whole circuit of 



