180 Mr. J. Blackwall's Exami?iation of 



the velocity of the particles such as would carry them in void 

 space from one extremity of the planetary regions to another 

 in a second of time, the ratio of their magnitude and mean 

 distance will approach that of the stars which form a nebula ; 

 whilst the mean space described in the medium by a particle 

 before the direction of its motion is altered by impingeing 

 against others, may be indefinitely smaller than any conceiv- 

 able magnitude. However extreme the rapidity of this action 

 may be considered, it is yet finite, and cannot therefore be 

 reckoned irrational or contrary to the institutions of nature. 

 It is the true primitive standard to which all velocities [upon 

 the hypothesis] may be compared, as from it every other 

 motion in the universe is derived. 



Professor CErsted, as far back as 1813, in his work on the 

 Identity of Electricity and Chemical Affinity, deduced, from 

 an extended series of experiments and general view of science, 

 " that all effects are produced by a fundamental power ope- 

 rating in different forms of action." It is remarkable that the 

 principle we have been explaining is in perfect unison with 

 the sentiments of this eminent philosopher. A medium is 

 supposed to envelope the universe, every particle of which is 

 a minute reservoir of power, which is conserved in the recti- 

 lineal and rotatory motion with which it is endowed. These 

 motions, by the introduction of the gross particles of different 

 substances, are alternately ti'ansformed into each other; and 

 thus the primordial power of ffiersted's doctrine by the varied 

 structure of the particles of matter " operates in different 

 forms of action," and is everywhere developed in the diversi- 

 fied series of natural changes. 



St. John's Hill, Edinburgh, April 14, 1831. 



XXIII. An Examination ofM.. Virey's Observations on Aero- 

 nautic Spiders, published i^i the Bulletin des Sciences Na- 

 turelles. Bij John Blackwall, Esq. F.L.S.* 

 'X'HE Bulletin des Sciences Naturellcs for July 1829, p. 131 — 

 •*■ 134, contains a notice, from the pen of M. Virey, of 

 my memoir on Aeronautic Spiders, printed in the Transac- 

 tions of the Linnaean Society, vol. xv. part ii. ; and it is parti- 

 cularly deserving of attention, that the author, by an extraor- 

 dinary misapprehension, originating apparently in an imper- 

 fect acquaintance with the F^nglish language, not only distorts 

 the facts I have promulgated and perverts the arguments 

 founded upon them, but even attributes to me opinions the 



♦ Read before the Linnaean Society, May 4, 1830 j and communicated 

 by the Author. 



very 



