day: geophysical research 253 



Dumpty's. But experiment has taught us that platinum crucibles, 

 magnesia furnace tubes enclosing an electrically-heated helix of 

 platinum wire, and electric temperature-measuring devices, pro- 

 vide a furnace in which nearly all of the important minerals can 

 be successfully studied, which is not enough to melt zinc, silver, 

 gold, copper, nickel or iron readily, and where any temperature 

 up to 1600° Centigrade can be maintained perfectly constant if 

 need be for several weeks. All these temperatures can be meas- 

 ured with no uncertainty greater than 5°. This equipment pre- 

 serves the chemical purity of the mineral studied, and enables 

 the temperature to be controlled and measured at every step of 

 the experimental work. Or an iridium furnace tube and an iri- 

 dium crucible can be substituted for platinum, the magnesia 

 supports can still be used, and we have it in our power to go on to 

 2000° C, which is quite sufficient for all the more important min- 

 erals which we know. 



The physicist has therefore found a suitable melting pot, and 

 means of ascertaining what goes on within the pot; but he at once 

 encounters another difficulty. Nature has provided us with 

 relatively few minerals of high chemical purity. If a natural 

 mineral is chosen for experiment, however typical it may be, 

 several per cent of other minerals may be expected to be present 

 with it, the effect of which is at present quite unknown. Now, 

 the first axiom of the investigator in a new field who desires to 

 undertake measurements which shall have a real value, is that 

 the number of unknown quantities in his equations must not be 

 greater than he can eliminate by his experimental processes; 

 in other words, he must begin with conditions so simple that the 

 relation between a particular effect and its cause can be absolutely 

 established without leaving undetermined factors. Having solved 

 the simple case, it is a straightforward matter to utilize this infor- 

 mation to help solve a more complicated one. If we would there- 

 fore reduce the mineral relations to an exact science, which is our 

 obvious purpose, it is necessary from the outset to prepare min- 

 erals of the highest purity and to establish their properties. Hav- 

 ing obtained such a pure mineral type, it may be, and often is, 

 in the power of the mineralogist and his microscope to determine, 



