98 Prof. A. M. Mayer on the Laws of the 



3. That the change in the adjustment of the collimator in- 

 troduced by the curvature of the prism is very small. One 

 prism, which I know to be exceptionally bad, gave a differ- 

 ence of a half per cent, in the focal length of the collimator. 

 It is not the change of focus introduced by the curvature of 

 the prism which makes the method inaccurate when the prism 

 is bad, but the difference in the change of focus in the two 

 positions of the prism. This is one of the reasons why it is 

 better to take the two positions of the prism not too far away 

 from minimum deviation. The small displacement of the 

 prism will only introduce a small variation in the focal length 

 due to the curvature of the faces. 



XIII. On the Morphological Laios of the Configurations formed 

 by Magnets floating vertically and subjected to the Attraction 

 of a superposed Magnet; ivith Notes on some of the Pheno- 

 mena in Molecular Structure which these experiments may 

 serve to explain and illustrate. By Alfred M. Mayer*. 



IN the May Number (1878) of this Journal (page 397 of 

 vol. v.), a short note was published on my experiments 

 with magnets floating vertically and subjected to the attraction 

 of a superposed magnet. The object of this paper is to present 

 accurate diagrams of the configurations formed by the floating 

 magnets, and to give the laws ruling these configurations, 

 with some notices of the peculiarities of these forms. At the 

 same time I will show how neatly these experiments illustrate 

 several phenomena in the molecular structure of matter. 



The Diagrams. — These diagrams show the configurations 

 formed by numbers of magnets extending from two to twenty. 

 They were obtained as follows: — The number of needles form- 

 ing a configuration were floated in a bowl filled to its brim with 

 water. The eye-ends of the needles, which protruded a short 

 distance beyond the tops of the corks, were of S. polarity. A 

 cylindrical magnet, 38 centims. long and 15 millims. in diame- 

 ter, was clamped in a vertical position, with its N. end at the 

 constant distance of 60 millims. above the tip of the needle, 

 which floated in the line of the axis of the magnet. I tipped 

 the ends of the needles with printer's ink; and when the con- 

 figuration had formed and was stationary, I brought down 

 upon the needles a piece of flat cardboard, and thus obtained 

 prints from nature. Around each of the dots on the card- 



* Communicated by the Author. 



