DETERMINATION OF MAGNETIC ELEMENTS, PHYSICAL LABORATORY. 69 
The study of any succession of transformations of a curve C 
can be replaced by the study of a transformation of the form 
above given. 
The calculation, the method of which I have shown, offers like 
the multiplication of quaternions an instance of operation associ- 
ative and not commutative. With regard to commutativity, any 
two consecutive letters can be interchanged under condition of 
changing the sign of the index of P which is either one of the 
letters or equal to the combination of the two letters. But it is 
not my intention to insist upon these points. 
In the next part of this paper I propose to determine the degree, 
class, and several singularities of the transformed curve. 
A DETERMINATION OF THE MAGNETIC ELEMENTS 
AT THE PHYSICAL LABORATORY, UNIVERSITY 
OF SYDNEY. Lat. 33° 53’14:1” 8. Long. 151° 10’ 49” E. 
By C. CoLERIDGE Farr, B.Sc. 
[With Plate II.] 
[Read before the Royal Society of N.S. Wales, June 1, 1892. | 
THE object which the Author had in view when making these 
observations was primarily the accurate determination of the 
elements for use in the Laboratory, and consequently nearly all 
of the observations were taken in the Laboratory, in a room in 
which previous observations have always been made. The pipes 
&c. at this end of the building are all of copper, and Professor 
Threlfall tells me that he tested the bricks when the building was 
being erected. There is however a wrought iron box in the form 
of a 500ibs. colonial mine case, at a distance of about twenty-eight 
