40 SCIENCE PROGRESS 
us to the already quoted abstract by Delesse in the Aznales 
de chimie et de physique, and misrepresents it by telling us 
that Delesse had only been able to separate magnetite from 
his rocks. (‘Eine Aahnliche Methode wandte Delesse zu 
Bestimmung des Magnetismus von Gesteinen und Muineralien 
an. Er konnte jedoch dadurch nur den Gehalt von Magneteisen 
bestimmen, denn dieses war es, welches bei seinen Versuchen 
entrahirt wurde.”) 
Like Fouqué, Doelter operated with magnetic fields of 
different intensities, obtained by varying the number of the 
Bunsen cells (2 to 8) which he used. In this way he examined 
many minerals, and gave a list showing the amounts by weight 
of the crushed minerals attracted to the poles of the magnet 
from approximately 0°25 gram in each case, varying the strength 
of the field according to the ease with which the mineral was 
attracted. This lst in some measure resembles that prepared 
earlier by Delesse, but is much less complete. Further, for com- 
parative purposes, Delesse’s method of using a field of constant 
intensity and a standard for comparison is decidedly preferable 
to the method adopted by Doelter. 
Another, though perhaps less effective method of comparison 
used by Doelter, was to operate with a field of constant 
intensity, and to determine the maximum distance from the 
poles at which grains of uniform size were lifted by the magnet. 
The results thus obtained are instructive, and are as follows: 
Millimetres Millimetres 
Magnetite. ; ‘ ce @Ju9) Augite (Santiago evi -" 30 
Hematite . : ; 5 $636 Hornblende ; 28 
Siderite . 3 : 5 oO Pleonaste . : 2) 357, 
Laeprite, -< : ; ve Ase Augite Ciena) . fea 
Almandine : ; he) Idocrase . : ‘ 2a 
Hedenbergite . ae Tourmaline ; ‘ ee 
Augite (Pico da Cri) e450 Actinolite  . 5 : « 27, 
Augite (Praya) . : Spee, Olivine ; : ‘ : 10°8 
Epidote . : : Pir ack) Vivianite . A ‘ 2, O°6 
Doelter also gives another list, as follows, in which those 
minerals under the same number have nearly the same magnetic 
value, starting with the most magnetic and ending with the 
least: 
1. Magnetite. 
2. Hematite, ilmenite. 
3. Chromite, siderite, almandine. 
