Intelligence and Miscellaneous Articles. 149 



effectively show gradations of light and shade and differences of 

 colour-distances, while in the fine cross-hatching, which delicately 

 indicates shading, the vertical line is carefully avoided. The only 

 sections where we thought gradation was not quite perfect are deep 

 blue (58,000) and grey (67,000) ; otherwise the plate seems to be 

 real perfection in a very difficult subject. 



A special note requests that if these colour-diagrams are used for 

 star-colour comparison in observatories (for which they seem very 

 appropriate), they may be viewed by a white light, a small Swan 

 lamp being preferred. 



Pages 25 to 28 comprise the author's summary of his Madeiran 

 results ; and with a genuine lament at the ignorance we are all in 

 of the chemical character of Great A, Great B, and the Alpha 

 Band (as evinced at the discussions of the British Association at 

 Southampton, 1882), he gives us his own views of it, to which we 

 must refer the reader. An Appendix prints Prof. Josiah P. Cooke's 

 valuable paper on the aqueous lines of the solar spectrum (Proc. 

 Amer. Acad, of Boston, vol. vii.p. 57); and a pretty vignette from 

 a sketch by the author adds the ornamental to the useful. 



That so elaborate and precise a work should have been carried 

 out by one hand, and under certain drawbacks to which Prof. 

 Smyth feelingly alludes, is not one of the least of the merits. To 

 be able to trace the recorded history of typical solar lines and 

 groups, with a final examination of them as shown in an almost ne 

 plus ultra instrument, and under splendid air-conditions hardly 

 attainable in this country, is no slight gain to spectroscopists. To 

 these in particular, as to scientists in general, ' Madeira Spectro- 

 scopic,' cannot fail to prove a standard work of the highest value. 



XXI. Intelligence and Miscellaneous Articles. 



ON AN ELECTRODYNAMIC METHOD FOR THE DETERMINATION 

 OF THE OHM. THE EXPERIMENTAL MEASUREMENT OF THE 

 CONSTANT OF A LONG INDUCTION-COIL. BY G. LIPPMANN. 



rPHE electromotive force employed in this method is produced 

 -^ by the relative displacement of two circuits, as in the well- 

 known experiment of M. Kirchhoff. The entire arrangement is 

 nearly the same as in the method of M. Lorenz. 



1. A movable frame rotates about one of its diameters with a 

 uniform velocity of n turns per second. It is placed inside a fixed 

 coil traversed by a current of intensity i, which at the same time 

 traverses the wire of which the resistance is sought. The induced 

 circuit is closed only for an instant, at the moment when the elec- 

 tromotive force passes through its maximum value e. At that 

 moment it is opposed to the difference of potentials which arises 

 between two points A and B on the wire, chosen so that there is 



