THE ELECTROMAGNET IN PETROGRAPHY 39 
In this memoir Fouqué described what he called a new 
mechanical process, by means of which he had been able to 
isolate the felspars of the Santorin lavas. In this process 
the rock was crushed and the crushings submitted to the 
action of a strong electromagnet. The iron ores, the ferro- 
magnesian minerals, and the partially differentiated ground 
of the rock were extracted, leaving a non-magnetic residue of 
felspar. The apparatus used by Fouqué consisted of an electro- 
magnet put into action by a Bunsen battery, and was essentially 
similar to the apparatus used by Pouillet, Delesse, and others. 
Fouqué also appears to have used a dynamo in some cases, 
as a substitute for a Bunsen battery. His results are very 
interesting, and prove convincingly the importance of the 
electromagnet as a means of isolating minerals. By its aid, 
and in conjunction with other methods, he was able to demon- 
strate that a given specimen of lava might contain quite a 
medley of plagioclases. He also proved that two varieties of 
pyroxene were present, both rich in lime, but differing con- 
siderably in the proportions of magnesia and ferrous oxide; 
also two olivines which differed in the amount of ferrous oxide 
present. 
It is quite clear, however, from the description which has 
been given of the work done by Delesse and others, that 
Fouqué, using the electromagnet in his researches, was using 
an old and not a new process. It seems scarcely credible that 
Fouqué could have been unaware of the work already done in 
this field by his fellow-countryman Delesse, and published in a 
journal so well known as the Annales des Mines. Even in the 
Mineralogie micrographique of 1879, in which Delesse’s other 
work is fully recognised, Fouqué’s error remained unrepaired, 
and it has unfortunately been persisted in by later text-book 
writers. 
Doelter,' following Fouqué, and apparently unaware of any 
important results other than those which the latter obtained, 
applied the electromagnet to the study of rocks and minerals. 
He wrongly attributes to Fouqué the priority for using an 
electromagnet in the systematic study of weakly magnetic 
rock-forming minerals. He makes matters worse by referring 
1 “Ueber die Einwirkung des Electromagneten auf verschieden Mineralien 
und seine Anwendung behufs mechanischer Trennung derselben,” Si¢zungberichte, 
Wien, 1882, Band Ixxxv. Abteilung i. 
