William Phillips

“ No reliance can be placed upon a solitary admeasurement taken upon the natural planes of one crystal, however brilliant and perfect they may appear; it is essential that several should be found to exhibit a perfect agreement, before it can be assumed that the actual value of any angle has been obtained. From one crystal of quartz, nearly perfect at both terminations and affording pretty clear reductions, I obtained six admeasurements of the same angle from its various planes. ”

“ But there is still another circumstance which forcibly shews the great difficulties attending the accurate admeasurement of the angles formed by the meeting of the natural surfaces of crystals, by subjecting those surfaces to either goniometer. It is not often found that the best selected afford incidences corresponding with the results obtained by calculation, even where we must be assured that calculation may be relied on ”

“ It cannot however, be doubted, that much of the labour attendant on the use of the reflecting goniometer in the measuring of the angles of crystals on their natural planes, will be spared, and that the results will be much more satisfactory, because more accurate, whenever cleavages can be obtained sufficiently brilliant for its use. ”