July 15, 1880] 



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terminals are joined to the two ends of an insulated wire, 

 part of the length of which is laid parallaj and near to the 

 conducting-wire of the dynamo-electric machine. M. 

 Deprez's new galvanometer shows by the most direct 

 evidence that this is the case, for when inserted in the 

 circuit of any dynamo-electric machine its needle is 

 observed to be in incessant vibration. 



The only instrument constructed previously to that we 

 arc about to describe, suitable for measuring strong cur- 

 rents, was the tangent galvanometer of Dr. Obach, the 

 essential feature in which consisted in the conducting- 

 ring being made movable about a horizontal diameter, 

 and therefore capable of being adjusted by inclining it at 



a greater or less obliquity to any degree of sensitiveness 

 between its maximum and zero, the horizontal component 

 of the m.-ignetic force of the current circulating in it being 

 zero when the ring was laid over into a horizontal plane. 

 M. Deprez's galvanometer is, however, a much more 

 handy instrument, its indications are almost instan- 

 taneous, and the deflections with very strong currents 

 are not unreasonably great. To secure this end it has 

 been necessary to make the needle of the instrument 

 very light, and at the same time to give it a veiy great 

 directive force by placing it in an artificial " field " of very 

 great intensity. The needle consists of twelve or fifteen 

 little pieces of soft iron wire set side by side transversely 



1 Deprez's Galvanometer for very strong currents. 



upon an axis of brass which is supported between 

 two pivots. The axis carries also a light hand or 

 index of straw or aluminium fixed at right angles to the 

 little iron needles. This compound needle is placed 

 between the limbs of a powerful permanent magnet 

 made of separately magnetised lamina superposed upon 

 one another (as suggested by Scoresby and Jamin), and 

 is thereby powerfully magnetised and directed into the 

 horizontal plane. The coils of conducting wire are carried 

 round the needle by being wound upon a light rectangular 

 frame which surrounds the needle, but lies within the 

 limbs of the permanent magnet. When a current passes 

 the needle jumps almost instantaneously to its position of 

 equilibrium, its oscillations being of extremely short 

 duration. M. Deprez has also tried needles made up of 



several superposed layers of the thin sheet iron used m 

 telephones, but the form shown in the figure is, on the 

 whole, the most satisfactory in practical operation. One 

 advantage possessed by the ins'rument is that it is inde- 

 pendent of gravity and of the magnetism of the earth, and 

 can therefore be used anywhere in any position. It will, 

 therefore, be found to be a very convenient instrument 

 for electrical engineers, but as its readings are not capable 

 of being translated into values representing current- 

 strengths by any simple trigonometrical function, sines 

 or tangents, it would require to be graduated empirically 

 by a process similar to the method of "calibration" 

 adopted for ordinary galvanometers by Melloni, before 

 it could be regarded as more than a convenient galvano- 

 scope. 



PROF. ir. H. MILLER 

 TT is only just to the memory of a man conspicuous 

 •'• within the circle of a not very large scientific class 

 that more than a passing word should be spoken over his 

 grave before the grass has grown on it. 



William Hallows Miller, whose life began with the 

 century, has lived far enough into it to experience what 

 is a happy fate for a scientific man ; he has seen the chief 

 work of his life bear fruit ; has seen the system he intro- 

 duced holding its place in the face of other systems, and 

 recognised more and more as a permanent addition to- the 

 agencies with which man may grapple with the problems 

 that nature presents to him ; he has seen it developed, but 

 not superseded. 



Crystallography was Miller's science. It had taken its 

 first shape in the hands of Haiiy in the decade of years 

 before he was born, and in those of Weiss, of Mohs, and 



especially of Franz Ernst Neumann and of Grassmann, 

 it had been receiving development during the years of 

 Miller's growth and manhood. 



The chair of mineralogy at Cambridge was filled pre- 

 viously to 1832 by Dr. Whewell, and a well-known 

 memoir on the geometrical treatment of crystal forms 

 which Dr. Whewell contributed to the Transactions of 

 the Cambridge Philosophical Society gave an impetus to 

 the study of crystallography in England which launched 

 Miller on his career. For, taking this memoir and Neu- 

 mann's treatise of 1S23 {Bcitnigc ::ur Krystallonomie) 

 as his starting-point. Miller, who was a pupil of Whewell's, 

 proceeded to develop a system of crystallography which 

 was not published till 1838, but which was the most 

 important work of his life. 



Dr. Whewell had already for some time recognised in 

 his pupil the ability and accuracy that marked him out 

 for the career he afterwards pursued, and in 1832 the 



