Intelligence and Miscellaneous Articles. 567 



the poles of the induction-coil ; the increase in quantity and 

 electromotive force was only made manifest to the eye by the em- 

 ployment of condensers in the secondary circuit. The results in 

 Table IV. were obtained by the employment of a Leyden jar of 

 large capacity. The increase in the quantity and electromotive 

 force was not only shown by the increased length of the spark, 

 but also by its increase in volume and its loud snap. The spark 

 consisted of a thick central bolt, surrounded by curious thin de- 

 tached sparks. An attempt was made to measure the increase of 

 light in Geissler tubes by Vierodt's photometric apparatus • but it 

 was found too inexact for this purpose — if, indeed, there was any 

 increase of light, which certainly remains to be proved. I know 

 of no results which bear upon the relation of the increase of light 

 to the increase of electromotive force of the induction-spark. 



Without condensers in the secondary circuit, however, the in- 

 creased electromotive force of the spark was shown by its greater 

 constancy in leaping over a given resistance of air. 



The results of this investigation can be thus summed up : — 



1. The application of thin p^tes of iron as armatures to two 

 straight electromagnets increases between four and five times the 

 strength of the spark produced by the surrounding secondary coils. 



2. The length of the spark is doubled, which is only shown by 

 the use of a condenser in the secondary circuit. 



3. The results show that it would be more economical to con- 

 struct induction-coils consisting of two straight electromagnets 

 constituting the primary circuit, and two fine coils constituting the 

 secondary circuit, with the use of thin plates of iron as armatures 

 to the electromagnets, than to distribute the same amount of wire 

 on one straight electromagnet as in the common form of Ruhmkorfi: 

 coil.— From the Proceedings of the American Academy of Arts and 

 Sciences, Feb. 9, 1876. 



a 



FELDSPAR " AND " FELDSTONE " VERSUS " FELSPAR " AND 

 " FELSTONE." 



Of the two modes of spelling the above mineralogical names, the 

 former is followed by the Germans of the present day, and the 

 latter by the English. 



"Felspar" (that is, the word without the d) occurs in the works 

 of Brooke and Miller (1852), Greg and Lettsom (1858), Mcol 

 (1849), Thomson (1836), Phillips (1816-1837), Allan (1814-1834), 

 Brooke (1823), Aikin (1807, 1815), Jameson (1804-1820), Kirwan 

 (1784, 1794) ; so that if good names can make any orthography 

 right, that of " felspar " is abundantly sustained. 



We find, however, among British mineralogists, Mr. John 

 Williams, in his ' Mineral Kingdom ' (1810), using the German 

 form " feldspar ;" and so also Mawes, in his ' Descriptive Cata- 

 logue ' (1821), and Townson, in his ' Philosophy of Mineralogy ' 

 (1798); and Nicholson, in his 'Dictionary of Chemistry,' like 

 Magellan in his translation of Cronstedt's 'Mineralogy' (1788), 



