66 EIGHTH REPORT— 1838. 



the inference, that the rate of annual decrease is less in Scot- 

 land than in England. Still, in the absence of more positive 

 data, I have not chosen to make any assmTiption ; and have 

 employed the one rate for the whole of the British Islands. 

 The general result in Scotland, /. e. the mass of observations 

 taken collectively, is independent of the amount of this re- 

 duction, the sum of the + and — reductions to the mean epoch 

 of the 1st of January, 1837, being very nearly the same: the 

 effect of a less rate of diminution than that adopted would be 

 to increase the dips deduced from the observations in 1836, and 

 to decrease those deduced from the observations in 1837 and 

 1838 ; and thus to give a rather more consistent aspect to the 

 whole, without sensibly altering the resulting isoclinal lines. 



No correction has been applied for the different hours of the 

 day at which the several observations were made ; but the hour 

 is in almost all instances recorded. Professor Phillips had 

 devoted several days of observation to the investigation of the 

 regular horary variations of the dip, and had obtained results 

 remarkably consistent, considering that they were derived from 

 observations with the ordinary dipping needle*; but the recent 

 invention of instruments specially adapted to this object, renders 

 it probable that the phenomena of the periodical changes will be 

 shortly determined with an accuracy hitherto unattainable : in 

 the mean time, it has appeared preferable to apply no correc- 

 tion on this account. It may be proper to remind the reader, 

 that the most perfect correction in this respect would still leave 

 unremedied the influence of the irregular fluctuations, which 

 there is great reason to believe frequently exceed in amount, and 

 occasionally counteract the ordinary periodical movements. 



I proceed now to give in detail the observations which com- 

 prise the first division of this report ; namely, those of the Dip 

 in England, Scotland, and Ireland. It will be convenient to 

 separate these into three sections, commencing with those of 

 England ; and it may here be remarked generally, that all the 

 latitudes and longitudes in this Report are taken from the maps 

 published by the Society for Diffusing Useful Knowledge. The 

 longitudes east of Greenwich are distinguished by the negative 

 sign prefixed. 



* Mr. Phillips's observations at St. Clairs and York, in the summer of 1837, 

 from 7 a.m. to 11 p.m., appear to indicate a morning maximum of dip at 9 or 

 10 a.m., an evening minimum about 8, with a difference of above 5 minutes, 

 the mean dip recurring about 3 p.m., and the line passing through the three 

 points nearly parabolic. 



