1882.] ^Ob [Chase, 



disturbed and eveu overthrown by tidal friction and retardation. Since g 

 is taken at the present locus of Jupiter's orbital projection, it seems possible 

 that the lunar disturbance, which Delaunay referred to tidal friction, 

 may have a secular period, which represents some function of Jupiter's 

 secular variations of eccentricity. If we take Leverrler's estimate of Jupi- 

 ter's present eccentricity, .0482388, and Stockwell's estimate of its secular 

 variation, .0608374, Sun's superficial gravitating acceleration is 1.037 g^ = 

 1.037 X 37.331G61 = 38.059. This gives p^ = 93.409,000 miles, if we take 

 the oscillatory estimate of Solar mass, and the British Nautical Almanac 

 estimate of Sun's apparent semi-diameter (?«(, = 331,770 m^^; p^ = 

 314.45^,q). Compare Note 356, e. 



297. Two Tidal Questions. 



No physical question can be regarded as satisfactorily settled, until all 

 the known facts which are likely to have any bearing on its solution 

 have been duly considered. Provisional hypotheses maj^ be very properly 

 adopted as occasional and temporaxy expedients, in order to fix new points 

 of departure, and facilitate the progress of investigation, but even they are 

 defective whenever they are obviously limited and partial. The cosmical 

 importance of harmonic motion, which Laplace demonstrated in his dis- 

 cussions of Jupiter's satellite system, as well as the further evidences of its 

 general physical importance which have been brought forwai'd by La- 

 grange, Fourier and Thomson, cannot be wisely set aside, even in a pro- 

 visional hypothesis, through any dogmatic assertion of a thermodynamic 

 requirement, which, if it is not compensated in pome way, may possibly 

 lengthen the terrestrial day by a minute interval, which has been variously 

 estimated, from go W to \l of a second in a year. Even if the requirement 

 w^as universally admitted, the relations of photodynamic precession (Note 

 293), indicate a possible harmonic acceleration which is manifoldly greater 

 than this problematical retardation. Before making any admission which 

 would call for a careful study of this possible acceleration, two questions 

 should be satisfactorily answered : 1. Are the tidal tendencies instan- 

 taneously adjusted? 2. Are the local tidal frictions limited to mere terres- 

 trial action, so that the conversion of motion into heat, at one point, is com- 

 pensated by a conversion of heat into motion at another? , 



398. Explosive Waves. 



Berthelot's discovery has already been suggested (Note 378, 6) as one 

 of the important topics for consideration in the study of rethereal correla- 

 tions. The velocity, i^g/i, which is indicated by the explosive energy of 

 HjO (Note 16), is (33.088 X 68878.3 X 1389.6 -- 9)* = 18473 ft. =3.49865 

 miles per second. This velocity is sufficient, under the normal atmos- 

 pheric pressure at Earth's surface, to produce aethereal waves which are 

 manifested by light, heat and chemical combination. We may accordingly 

 look for like phenomena whenever "subsiding" particles penetrate the 



PROC. AMEU. PHILOS. SOC. XX. 113. 3c. PRINTED NOVEMBER 34, 1882. 



