346 DR. C. CHREE: ANALYSIS OF RESULTS FROM THE KEW MAGNETOGRAPHS 
previously'^ for Kew from the five yeai’S 1890-4. At the same time, the ranges now 
found are somewhat conspicuously less than the ranges, L''22 in D and 12‘9y in H, 
oljtained on the previous occasion. 
Tn the case of D and H, the variation in the mid-monthly values in Taide IV. 
seems altogether too regular to he ascribed to chance, and even in I and V something 
more than chance seems involved. It must lie allowed, however, that in these last 
two elements the value for March stands out in a way one can hardly suppose to he 
truly representative of Nature, and in the case of V, the tendency to negative values 
in the latter lialf of the year, and the apparent jump from December to January, are 
somewhat suggestive of an under-estimate of the true secular change. 
§ 12. Due possibility to wliich attention should be drawn is that an annual 
inequality may he in no way ascribalile to erroi's of observation, or of estimation of 
tlie secular change, and yet be absolutely fictitious so far as terrestrial magnetism is 
concerned. For example, if the distant mark used in absolute observations of D 
shifted in any way dependent on the temperature of the air, or on the temperature 
or moisture of the soil, an apparent annual inequality would ensue. A similar result 
would happen in the case of H if tlie law of variation with temperature in the 
moment of inertia of the collimator magnet were wrongly assumed. In the present 
case I have applied an elaliorate check—whose description would take me too firr 
aheld—calculated to disclose any apprecialile uncorrected effect of temperature on 
absolute observations of H, and the conclusion it led to was that if any such efiect 
existed it was small compared to the range found for the annual inequality. It is 
also noteworthy that in all tlie elements the beginning of the month data indicate a 
large semi-annual term in the annual ineipiality, wliich is not what one would expect 
to find if the true cause of the phenomena were moisture or temperature. 
Non-cijclic Effect. 
§ 13. In virtue of the secular clianges shown in Table III., the value of an element 
should exceed its value 24 hours earlier, on tlie average tliroughout the period now 
dealt mth, by the following amounts :— 
I). 
1 . 
H. 
W. 
N. 
Y. 
T. 
-O-OIG 
-6-007 
+ O-OTy 
-O-OGy 
+ 0•09y 
- 0•OGy 
-0-03y 
These quantities are all mucli less than can be directly measured on the magneto- 
grams. Such as they are, however, they contribute to what I have termed the 
“ non-cyclic effect.”! 
* ‘British Association Report for 1895,’ p. 226. 
t ‘ Plritish Association Report for 1895,’ p. 210. 
