488 REPOBT— 1889. 



empiricism has no place with it. Photography, on the other hand, has laboured under 

 the disadvantage that, though it is subject to measurement, the factors of exactitude 

 have been hitherto absent. In photography we have to deal with molecules the 

 equilibrium of whose components is more or less indifferent according to the process 

 used ; again, the light employed is such a varying factor that it is difficult to com- 

 pare results. Perhaps more than any other disadvantage it labours under is that 

 due to quackery of the worst description at the hands of some of its followers, 

 who not only are self-asserting, but often ignorant of the very first principles of 

 scientific investigation. Photography deserves to have followers of the highest 

 scientific calibre ; and if only some few more real physicists and chemists could be 

 induced to unbend their minds and study the theory of an applied science which 

 they often use for record or for pleasure, we might hope for some greater advance 

 than has hitherto been possible. 



Photography has been called the handmaid of Art ; I venture to think it is even 

 more so the handmaid of Science, and each step taken in perfecting it will render 

 it more worthy of such a title. 



The following Reports and Papers were read : — 



1. Fifth Report of the Committee for Promoting Tidal Observations in 

 Canada. — See Reports, p. 27. 



2. Seport of the Committee for preparing Instructions for the Practical 



Work of Tidal Observation. 



3. Fifth Report of the Committee for the Harmonic Analysis of Tidal 



Observation. 



4. On the Heliocentric Longitudes of Com.''tic Perihelia.^ 

 By Henry Muirhead, M.I)., LL.D. 



In 1880 I read a paper to the Philosophical Society of Glasgow (see vol. 13, 

 pp. 34-46) on the relations of sunspot maxima and minima to the bearing of 

 Jupiter to the sun's line of flight in space. In that paper I called attention 

 to the longitudinal relations which the perihelia of comets seem to bear to our 

 primary's line of travel, and pointed out that, taking the two groups of comets 

 given by Mr. Hind in the ' Encyclopoedia Britannica ' (article ' Comet '), with 13 

 others which I was able to find in ' Nature,' up to date — in all 35 — and arranging 

 them circularly according to their heliocentric longitudes, they very largely 

 crowded into the quadrants which the sun's line of flight bisects in his progress 

 in the direction of helial longitude 263|°. Attention was also called to certain 

 relations of some phenomena of terrestrial magnetism and the three larger planets 

 crossing the sun's line of flight. 



Recently I have gone over the succeeding volumes of ' Nature,' noting all the 

 cometic perihelia recorded therein (41 more). These, too, show a tendency to 

 avoid the normals to the line ; so much so, indeed, that, taking the central Jlank 

 octants, the quadrant thus constituted shows only 9 cometic perihelia out of a total 

 of 75. 



Moreover, in Guillemin's ' AVorld of Comets ' (Glaisher's Translations, p. 186), 

 we are furnished with a total of 257 cometic perihelia given below. In this 

 table, in the 60° intervening between 150° and 210° forming the sinister flank 

 division {of the plate) we have the numbers 14 + 10 = 30, and between 330° and 30° 

 the dexter flank division 8 + 17 = 25. Well, neglecting the intermediate twelfths 

 which show a remarkably intermediate character, viz., 24, 21, 21, 22, let us now 



' Will appear in, extenso in vol. xxi. of the Proc. Glas. Phil, Soc. 



