14 Capt. H. G. Lyons. [June 6, 



W. 4° + April, 1896. 



Hours. 



1. 



2. 



3. 



4. 



5. 



6. 



7. 



8. 



9. 



H 



8 



22-3 



22-8 

 



22-8 



21-5 



- 

 21 -0 



19 -9 



20-5 



20-8 



19 -2 



9 





24-4 





22 3 













10 





26 -6 











21 -5 



— t 



20 -9 



11 



24-6 



28 -0 



27 -1 





23 7 



23 -5 



24-6 





22 -8 



Noon 



25 *5 







25 -5 



24-9 



24-8 



26 -0 



24-6 



24-6 



1 



2 



24 -6 



28-2 



26-0 



24 -6 



24-6 



24-2 



25-8 



26 -0 



22-9 



3 





















4 





24-6 















— 



5 



22 9 





22-8 



22 -1 



223 



21-0 



22 -8 



21 -9 



22 -6 



IV. Magnetic Observations at Heiwan, near Cairo. 

 (See table on opposite page.) 



V. Secular Variation. 



As many early observations as it has been possible to find in various 

 works have been collected in the following tables for the purpose of 

 determining the average annual rate of change. Generally the decli- 

 nation appears to have been annually decreasing by about 6' to 7' in 

 the first half of the century, becoming, however, 3' to 4' only in the 

 second half. For the dip the available observations are very few ; but 

 from those at Alexandria and at the Great Pyramid, Giza, the rate of 

 decrease appears to be about V to l'*5 annually. For the horizontal 

 force the observations are too few, and give results which are not very 

 concordant. 



The observations before June, 1894, were made with the declina- 

 torium, so that those made at later dates are more reliable, since a 

 Kew pattern magnetometer with a unifilar suspension was used. 



The values obtained cannot be considered as laying claim to a high 

 degree of accuracy, seeing that in most cases the hour of observation 

 is not given in the older observations ; still in most cases the number 

 of years elapsed is sufficiently great to reduce the error thus intro- 

 duced into the value for the annual change to small dimensions. 



(Tables are printed on pp. 16, 17 and 18.) 



