﻿4>76 Dr. A. M. Mayer on a Method of Fixing, 



elevations in newly drawn-out capillary tubes. The angle of 

 liquids against pure glass surfaces is only in rare cases =0. 



13. If two liquids are placed one above the other in a capillary 

 tube, then the weight of liquid raised above the common level de- 

 pends on the form of the free surface of the upper liquid o and 

 the common surface of the upper and lower liquids o and u. 



14. The weight of liquid raised above the common level is never 

 determined by the lower liquid u alone, as Poisson says ; in many 

 cases, on the contrary, when the liquids o and u are miscible in 

 all proportions, by means of the upper liquid alone. 



15. The mean elevation of the liquids o and u admits of being 

 estimated from the values a and a ou measured on flat drops or 

 bubbles when the angle made by the free and that made by the 

 common surface of both liquids with the side of the tube are known. 

 Only in a few cases is this angle 0° or 180°. 



16. The observations of elevations in capillary tubes and on flat 

 drops of a liquid or drops falling out of vertical tubes in air may 

 easily give too small a value of the capillary constant, since foreign 

 substances diffused through the atmosphere in the form of vapour are 

 condensed on the curved capillary surface, and the thin layer of 

 liquid arising therefrom diminishes the tension of the free surface. 

 This source of error is greater at ordinary than at high tempera- 

 tures, is more considerable in liquids with great capillary con- 

 stants than in those with small, and accounts for the too small 

 values of capillary constants found by earlier observers in some 

 liquids, as mercury and water. 



17. This condensation of moisture on the surface of liquids ex- 

 plains the different forms of lens-shaped drops of water on mer- 

 cury and the so-called Moserian figures. 



LX. On a Method of Fixing, Photographing, and exhibiting the 

 Magnetic Spectra. By Alfred M. Mayer, Ph.D.* 



THE figures produced in iron-filings, when these are set in 

 momentary vibration on a surface placed over a magnet, 

 have received considerable attention from natural philosophersf. 

 The geometrical discussion of these spectra made by Lambert, 

 Roget, and others have developed their symmetrical properties, 

 and thereby have evolved the law of that action which emanates 

 from the magnet. De Haldat has used them as a means of ex- 

 ploring the distribution and intensity of the effect of juxtaposed 

 magnets variously arranged. But above all have the researches 

 of Faraday and W. Thomson on " the magnetic field," and on 



* From the American Journal of Science and Arts, vol. i. April 1871. 



t See a neat " Demonstration par le calcul des courbes magnetiques de 

 la loi de Finverse du carre de la distance," by M. Cellerier, published as a 

 note on p. 592, vol. i. of De la Rive's Traite d'Eiectriciti. 



