Intelligence and Miscellaneous Articles, 243 



the pleasure of exhibiting are more striking and conclusive than any 

 which have been previously obtained. — Silliman's American Journal 

 for January 1866. 



NOTE REGARDING THE DECREASE OF ACTINIC EFFECT NEAR THE 

 CIRCUMFERENCE OF THE SUN, AS SHOWN BY THE KEW PIC- 

 TURES. BY MESSRS. WARREN DE LA RUE, STEWART, AND 

 LOEWY. 



The remarks which we ventured to make in the last para- 

 graph of our ' Results on Solar Physics,' recently published, have 

 induced us to examine the Kew pictures, as regards the decrease of 

 actinic effect from the centre to the circumference of the sun, to 

 which decrease we may give the name of atmospheric effect, since it 

 is without doubt caused by the presence of a comparatively cold 

 solar atmosphere. 



In conformity with our views, this atmospheric effect ought to be 

 greater at the epoch of maximum than at that of minimum spot-fre- 

 quency ; and furthermore, if there is any reference to ecliptical lon- 

 gitudes in the behaviour of spots — that is to say, if at any time the 

 spots on the sun attain their maximum at any ecliptical longitude — 

 there ought (according to these views) to be a greater amount of 

 absorbing atmosphere at the same longitude, since such an atmo- 

 sphere is supposed conducive to the outbreak of spots. 



There is reason to think that spots attain their maximum in the 

 ecliptical longitude opposite to that where Venus exists ; so that we 

 might expect (according to these views) a diminution in atmospheric 

 effect in the same longitude as Venus, and an increase in the effect 

 in the longitude opposite to Venus. 



If therefore Venus be at the longitude of the left limb of the 

 sun, this limb should exhibit less atmospheric effect than the right 

 limb ; and if Venus be at the right limb, we should have most atmo- 

 spheric effect at the left limb. 



It is only the under-exposed pictures that are available for a re- 

 search of this nature, since an over-exposure tends to do away with 

 the atmospheric effect. 



Without giving any hint of our views, Mr. Beckley was requested 

 to select some of the last Kew pictures taken in 1859, a year of 

 maximum spot-frequency, and to compare them with those taken in 

 1864 and 1865, periods of minimum spot-frequency ; and he came to 

 the conclusion that there was more atmospheric effect in 1859 than 

 in the years 1864 and 1865. 



Furthermore, Mr. Stewart, in conjunction with Miss Beckley, has 

 looked over all the pictures taken at Kew from May 1863 to the 

 present date ; and this examination was made in such a way that 

 the results could not derive any bias from the opinion of Mr. 

 Stewart as one of the joint authors of the ' Researches on Solar 



