TRANSACTIONS OF THE SECTIONS. 39 



would bo able to call them to mind themselves and apply to them reasoning precisely 

 similar. 



The author attached great importance to the question, because he thought that 

 in erroneously considering heat to be molecular vibration, we lost sight of the true 

 explanation of electricity, which he believed to be neither more nor less than that 

 very vibration or molecular' motion which the dynamic theor}' called heat. 



On the Wave Theory of Light, Heat, ^-c. By Dr. Hi^nry Hudsox. 



Huyghens (to explain double refraction) assumed a second vibrating medium as 

 consisting of "the molecules and ajther conjointly; " and Fresnel's grand theory 

 rests on the same foundation. As molecular vibrations in air (sound-waves) are 

 10,000 times longer and 809,000 times slower than etherial waves, the author 

 rejects this combination as inadequate to account for the very minute dift'erence in 

 the retardation of the doubly refracted rays in crystals. lie then adduces several 

 cases, especially in polarized light, une.vplamed on Fresnel's theory, and proceeds to 

 show that all the difficulties in Fresnel's theory can be removed by considering the 

 " sether " to consist oHwo media, each possessed of equal and enormous self-repulsion, 

 and both existing in equal quantities throughout space, being also mutually 

 indifferent (neither attracting nor repelling), and that their vibrations conse- 

 quently always take place in perpendicular iilanes. lie then suggests as an experi- 

 mental test of this view, " that the ordinary refracted ray, through Iceland spar, 

 cannot be made to show any phenomena of Interference with the apparently 

 similarly polarized ray obtained by total reflexion from glass," because, on this 

 ^'icw, their vibrations are in different media. After discussing many curious and 

 interesting questions, he pointed out that the two Electricities fulfil the requirements 

 of the theory, being, as he asserts, mutualhj indifferent, and constitute the tether. 

 Electrical phenomena the author would explain by the existence of '' waves of 

 translation as well as " waves of vibration " aftecting the molecules of bodies — the 

 former being most prominent in " statical phenomena " (induction especially), and 

 the latter more generally observed in what is denominated " the electric current." 



Optics. 



On the Immersion Method of Illumination of the Microscope. 

 By Dr. John Bakkee. 

 After showing the defects of the present methods as exhibiting merely shadows 

 and caustics of reflection and refraction, and markings resulting very often from the 

 relative opacity and ti'ansparency of the parts of an object, the author was led to 

 believe, from the study of the way in which objects are best illuminated for unas- 

 sisted vision, that this was the method to which we should endeavour to ap- 

 proximate in the illumination of microscopic objects. The adaptation of the immer- 

 sion plan in condensers of various forms seemed to him to best fulfil these require- 

 ments. The object would be illuminated by very oblique light, the oblique rays 

 being most economized, undergoing less loss and less dispersion. The author brought 

 forward several forms of this mode of illumination, in which a flat-topped paraboloid 

 was used, which, he stated, gave very good results with a two-thirds used with 

 binocular microscopes ; another was a flat-topped paraboloid to be used above the 

 object, and in the centre of which (the glass paraboloid) the power was placed so as 

 to light up the object under the highest powers with reflected light. The ordinary 

 achromatic condenser, too, he thought, might be greatly increased in value by 

 adapting it to the immersion plan. 



On the New Binocular Microscope, By S. Holmes. 

 The author showedthat the views of objects seen through a microscope, being 



