PHILOSOPHICAL TRANSACTIONS 
I. On the Determination of Verdet’s Constant in Absolute Units . By J. E. H. Gordon, 
B.A., Gonville and Caius College, Cambridge. — ls£ and 2nd Memoirs*. Commu- 
nicated by J. Clerk Maxwell. 
Received June 5, — Read June 15, 1876. 
[Plate 1.] 
[Note. — The whole of this work has been done under Professor Clerk Maxwell’s superintendence ; he 
suggested the method and nearly all the details, and any merit which the investigation may have belongs to 
him. He is, however, in no way responsible for any errors there may be in the numerical results.] 
Introdtj CTORT 
Description of Instruments. 
The Helix 
The Dynamometers 
The Polarizing Apparatus 
The Analyzing Apparatus 
The Jellett Prism 
The Divided Circle 
The Galvanometer 
The Tube 
The Experimenting Table 
Measurement of Horizontal Distances 
The Experiments. 
Determination of Number of Windings 4 
Determination of Areas 9 
Calculation of Strength of Current in Helix . . 14 
Eormula for w 14 
Page 
Tan S 16 
Determination of the Meridian 16 
Verification of the Meridian 17 
The Light 17 
The Optical Experiments 19 
Value of H 20 
Vibration Experiments at Kew 22 
Vibration Experiments at Pixholme 22 
Corrections to Virration Time. 
Temperature Correction 27 
Torsion Correction 28 
Clock Rate 29 
Corrected Vibration Times 30 
Mean Values of H at Pixholme 32 
Einal form and value of w 15 & 33 
Conclusion 33 
| Appendix. — Analysis of bisulphide 34 
Contents. 
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* In a former memoir which Prof. Maxwell did me the honour of communicating to the Royal Society, and 
which was read June 17th, 1875, the object of this research was explained and a result given. 
The method employed, however, was faulty in several respects, the two most important of which were : — 
1st. The rotations produced were exceedingly small, so that a slight error in the determination of the plane 
of polarization introduced a large error into the results. 
2nd. A tangent-galvanometer was used to determine the strength of the current. 
In the experiments which are the subject of the present Memoir I have, at Prof. Maxwell’s suggestion, used 
MDCCCLXXVII. B 
