CAPELLA

, a bright star of the first magnitude, in the left shoulder of Auriga.

CAPILLARY Tubes, in Physics, are very small pipes, whose canals are exceedingly narrow; being so called from their resemblance to a hair in smallness. Their usual diameter may be from 1/20 to 1/50 of an inch: though Dr. Hook assures us that he drew tubes in the flame of a lamp much smaller, and resembling a spider's thread.

The Ascent of Water &c, in capillary tubes, is a noted phenomenon in philosophy. Take several small glass tubes, of different diameters, and open at both ends; immerse them a little way into water, and the fluid will be seen to stand higher in the tubes than the surface of the water without, and higher as the tube is smaller, almost in the reciprocal ratio of the diameter of the tube; and that both in open air, and in vacuo. The greatest height to which Dr. Hook ever observed the water to stand, in the smallest tubes, was 21 inches above the surface in the vessel.

This does not however happen uniformly the same in all fluids; some standing higher than others; and in quicksilver the contrary takes place, as that fluid stands lower within the tube than its surface in the vessel, and the lower as the tube is smaller. See Philof. Trans. N° 355, or Abr. vol. 4, pa. 423, &c, or Cotes's Hydr. and Pneum. Lect. pa. 265.

Another phenomenon of these tubes is, that such of them as would only naturally discharge water by drops, when electrisied, yield a continued and accelerated stream; and the acceleration is proportional to the smallness of the tube: indeed the effect of electricity is so considerable, that it produces a continued stream from a very small tube, out of which the water had not before been able to drop. Priestley's Hist. Electr. 8vo. vol. 1, pa. 171, ed. 3d.

This ascent and suspension of the water in the tube, is by Dr. Jurin, Mr. Hauksbee, and other philosophers, ascribed to the attraction of the periphery of the concave surface of the tube, to which the upper surface of the water is contiguous and adheres.