Fluorescence and Arrangement of Molecules. 473 



wires on insulating stands of the paraffin-bottle form, the 

 cells, resistance-boxes, galvanometer, &c. on sheets of glass, 

 themselves resting on small cylinders of paraffin. The insula- 

 tion of the handles of the keys requires attention. Paraffin 

 keys are much better than ebonite ones. 



In pushing the sensitiveness of the galvanometer beyond 

 this point, the following precautions should be observed be- 

 sides those already mentioned. The arrangement for sup- 

 porting the magnets should be quite independent of the 

 arrangement for supporting the suspension. The base of the 

 instrument should be of gun-metal and all the framework of 

 metal. The adjustments of the controlling magnets must be 

 capable of being made with extraordinary accuracy. The 

 mirror must be good enough to be used in a telescope. The 

 quartz fibre should be at least six feet long ; it must be 

 cemented to its connexions with hard paraffin. The whole 

 apparatus should, we think, be placed in a thick soft iron 

 cylinder, but about this we are not sure. We are tolerably 

 certain, however, that it is in anybody's power to construct a 

 galvanometer on these lines with a sensitiveness of 10~ 13 

 amperes per scale-division and a time of swing of about 40 

 seconds. Such an instrument, however, could only be used 

 in a tolerably non-magnetic building, and one steady enough 

 to be free from the vibration caused by people walking about. 

 Our best results were got at night and on Sundays, and this 

 in spite of the room having a concrete floor reposing on 

 twenty feet of broken stone and all the instruments being 

 supported on slate benches. 



As to the results quoted, no discussion will be given here 

 as we are investigating pure samples of sulphur. It may, 

 however, be mentioned that the resistance depends con- 

 siderably on the time the current has been flowing, on the 

 electromotive force, and on the temperature. 



LVI. On the Relation between Fluorescence and Arrangement 

 of Molecules. By B. Waltek*. 



IT is well known that the intensity of the fluorescent light 

 from solutions of many fluorescing materials at first 

 increases with the dilution and afterwards decreases again. 

 In order to understand this phenomenon rightly one must 

 compare, for different degrees of concentration, as Stokes 



* Communicated by the Author, and translated from the MS. by James 

 L. Howard, D.Sc. 



