CAPILLARY ATTRACTION. 



Mary the distance between the plates in the preceding ex- 

 pi-riment, the water will rise in it to the same height 

 V *V^^ as between the plates. See Ncwton'b Oj>tt> 



Exp. '2*. If a fluid is either elevated or depressed 

 between two vertical and parallel planes, the planes 

 will tend to approach each other. 



Exp. I 2i). "If two plane polished plates of glass, 

 three or four inches broad, and twenty or twenty-five 

 long, be laid one of them parallel to the horizon, the 

 other upon the first, so as at one of their ends to 

 touch one another, and contain an angle of about 10 

 or 15 minutes, and the same be first moistened on 

 their inward sides with a clean cloth dipped into oil 

 of oranges, or spirit of turpentine, and a drop or two 

 of the oil or spirit be let fall upon the lower glass at 

 the other end ; so soon as the upper glass is laid down 

 upon the lower, so as to touch it at one end as above, 

 and to touch the drop at the other end, making with 

 the lower glass an angle of about 10 or 15 minutes ; 

 the drop will begin to move towards the concourse 

 of the glasses, and will continue to move with an ac- 

 celerated motion till it arrives at that concourse of 

 the glasses. For the two glasses attract the drop, 

 and make it run that way towards which the attrac- 

 tions incline. And if when the .drop is in motion, 

 yqu lift up that end of the glasses where they meet, 

 and towards which the drop moves, the drop will 

 ascend between the glasses, and therefore is attracted. 

 And as you lift up the glasses more and more, the 

 drop will ascend slower and slower, and at length 

 rest, being then carried downwards by its weight as 

 much as upwards by the attraction. And by this 

 means you may know the force by. which the drop 

 is attracted at all distances from the concourse of the 

 glasses. Now, by some experiments of this kind, 

 (made by Mr Hauksbee,) it has been found that the 

 attraction is almost reciprocally in a duplicate pro- 

 portion of the distance of the middle of the drop 

 from the concourse of the glasses, viz. reciprocally in 

 a simple proportion, by reason of the spreading of 

 the drop, and its touching each glass in a larger sur- 

 face ; and again reciprocally in a simple proportion, 

 by reason of the attraction growing stronger within 

 the same quantity of attracting surface. The attrac- 

 tion therefore within the same quantity of attracting 

 surface is reciprocally as the distance between the 

 glasses. And therefore, where the distance is exceed- 

 ing small, the attraction must be exceeding great." 

 Newton's Of lies, p. 36'7. 



i). 30. If the plates in 7'.r/;. 26. are inclined to 

 each other at a small angle, and are immersed in 

 water with the line of their intersection vertical, the 

 water will ascend between them, and will form a beau- 

 PLATP CX. t '^ curve - This experiment is represented in Fig. 6. 

 y,.,. G. By measuring the ordinates and abscissse of the curve 

 a h, Mr Hauksbee found it to be the common Apol- 

 lonian hyperbola. This indeed follows from Exp. 26, 

 from which it appears that the altitudes are reciprocally 

 as the distances of the plates. The heights of the fluid 

 being the ordinates of the curve, and the distances of 

 the plates being as the abscissae, the ordinates are in- 

 versely proportional to their respective abscissa, which 

 is the property of the common hyperbola. 



The preceding experiments, though numerous 

 and varied, are obviously insufficient to form a pro- 

 per basis for a philosophical theory. The enor- 

 mous discrepancy among some of the results, as ob- 



VOL. V. PART II. 



409 



mined by different philo-.ophen, i completely be- 

 wildering ; and, if we did not know that they were 

 all made in the eighteenth century, we should have 

 imagined that they were obtained in the dullest age 

 of experimental philosophy. The height to which 

 water ascends in a capillary tube, the diameter of 

 whose bore is Tl ^j. of an inch, hag been stated in the 

 latest elementary works upon natural philosophy, at 

 5 inches and 3-tenths, according to the experiments 

 of Mr Atwood ; while, according to the more recent 

 experiments of Messrs Hauy and Tremery, made at 

 the desire and under the eye of La Place, the water 

 rises only to the height of 2 inches and 1 -tenth. The 

 difference between these quantities amounts nearly 

 to two-thirds of the whole ; and what is still more 

 perplexing, we are unacquainted with the particular 

 manner in which the experiments were made, so that 

 we are unable to discover any ground of preference, 

 from the variou : precautions which were probably 

 taken by the different observers to ensure accuracy, 

 and to avoid error. 



Under these circumstances, the writer of this ar- 

 ticle resolved to repeat the experiments himself; and 

 he was particularly anxious to bring his apparatus 

 into such a state, that he could always obtain the 

 same result by repeated trials. After much trouble, 

 he succeeded in this attempt to such a degree, that 

 the water uniformly stood at the same height in the 

 tube ; and the same degree of accuracy was obtained 

 for the other fluids, which were submitted to exami- 

 nation. To enable the reader to form a proper esti- 

 mate of the degree of confidence which these results 

 should inspire, we shall describe the precautions 

 which were found necessary in the course of the expe- 

 riments. 



Having obtained a glass .tube 7.9 inches long, 

 and of a uniform circular bore, we took a wire of a 

 less diameter than the bore of the tube, and formed a 

 small hook at one of its ends. This hook was fasten- 

 ed to the middle of a worsted thread, of such a size, 

 as when doubled, to fill the bore of the tube. The 

 wire was then passed through the tube, and the 

 worsted thread drawn after it; and when the whole 

 was plunged in an- alkaline solution, the worsted 

 thread was fixed at one end, and the tube was drawn 

 backwards and forwards, till it was completely de- 

 prived, by its friction on the thread, of any grease or 

 foreign matter which might have adhered to it. The 

 tube and thread were then taken to clean water, and 

 the same operation was repeated. 



When the tube was thus perfectly cleaned, it was 

 fixed vertically, by means of a level, in the axis of a 

 piece of wood D, supported by the arm AD, fix- 

 ed upon a stand AB; and it was also furnished with 

 an index mn, which was- rnoveable to and from the 

 extremity b. On the arm CE, moveable in a ver- 

 tical direction by the nut C, wae placed a glass vessel 

 F, containing the fluid, and nearly filled with it. The 

 nut C was then turned till the -extremity b of the 

 tube touched the surface of the fluid, which was in- 

 dicated by the sudden rise- of the liquor round its 

 sides. The fluid then rose in the tube till it remain- 

 ed stationary, and the index mn was moved till its ex- 

 tremity n pointed out the exact -position of the upper 

 surface of the fluid. In this situation, the distance 

 n b was a measure of the ascent of the liquid above 

 its level in the vessel E. In order to ascertain, how- 

 3* 



Attract iun 



Account of 

 Dr Brewi- 

 ter' ex- 

 periments 

 on capilla- 

 ry attrac- 

 tion. 



PLATK CX. 

 Fig. 7. 



