PROCEEDINGS 
OF THE 
ROYAL SOCIETY OF EDINBURGH. 
SESSION 1908-9. 
Part III.] VOL. XXIX. [Pp. 129-192. 
CONTENTS. 
NO. PAGE 
IX. On the Conditions for the Reversibility of the Order of Partial 
Differentiation. By W. H. Young, Sc.D., F.R.S. ( Com- 
municated by J. H. Maclagan Wedderburn, D.Sc.), . 136 
{Issued separately March 2, 1909.) 
X. Laboratory Note on a Study of Polarisation by means of the 
Dolezalek Electrometer. By A. F. Ewan, Physical Laboratory, 
Edinburgh University. ( Communicated by Professor J. G. 
MacGregor), . . . . . . .165 
{Issued separately April 12, 1909.) 
XI. A Special Form of Photographic Camera for Recording the 
Readings of the Scales of Scientific Instruments. By James 
Robert Milne, D.Sc., . . . . . . 176 
{Issued separately April 17, 1909.) 
XII. On an Improved Form of Magnetometer and Accessories for 
the Testing of Magnetic Materials at Ditferent Temperatures. 
By James G. Gray, B.Sc., Lecturer on Physics in the 
University of Glasgow, and Alexander D. Ross, M.A., B.Sc., 
Assistant to the Professor of Natural Philosophy in the 
University of Glasgow. {Communicated by Professor 
A. Gray, F.R.S.), ...... 182 
{Issued separately April 17, 1909.) 
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