348 mi. C. CIIKEE: ANAT.YSIS OF KESULTS FKO*M THE KEW .MAGNETOGRAPHS 
As tlie balance had usually been altered at the same time, it was difficult to arrive at 
direct conclusiojis as to the true effect on the curve ordinates. A comparison, 
however, of the cuiwe ordinates after the scale determinations in January with those 
in the followiiip' Deceml)er, on seven years wdren no intermediate chano-e had heen 
made, showed a decrease in the ordinate due to instrumental causes at the average 
rate of 24y a year. The change was in the same direction each year. An annual 
change of — 24y gives a mean non-cyclic effect of — 0‘07y per day. Combining 
instrumental causes with true secular change, we get a non-cyclic effect of about 
— 0'13y per day. This represents, as we shall see, about 15 per cent, of the average 
non-cyclic effect actually oljserved on quiet days. 
§ 14. There is unavoidahly some uncertainty in the estimates of artificial non-cyclic 
effects, and I have attempted no correction to the results as observed. 
'llie H and V magnets would probably be more exposed to losses ot magnetism 
during magnetic stonns than on ordinary occasions, and the chances are that any 
estimate we should make of the contriljution from instrumental causes to the observed 
non-cyclic effect on (piiet days would be in excess, in the case at least of V. Again, 
as will he seen presently, we have to correct the observed readings of the curves for 
non-cyclic efiect, and, so far as the corrections are concerned, wdiat Ave have to deal 
Avith is the entire effect, Avhatever its sources. It is desirable to haAm on record the 
actual corrections made, so that anyone can reproduce the actual observation results 
Avlio Avishes to do so. 
The quantities then actually recorded under the heading “ non-cyclic efiect ” in the 
folloAving tables V. to X. represent the algeljraic excess of the recorded A’alue of an 
element at the second midnight over that at the first midnight of a “ quiet ’ day, 
irrespective of the source to Avhich the increment is due. 
In Table X., as subsequently, the year is sub-dl\'ided into three seasons— 
“ Winter,” comprising the four months Novemljer, December, January, February; 
“E(|uinox” ,, ,, ,, March, April, 8e})tember, October; 
“Summer” ,, ,, ,, May, June, July, August. 
