108 MTOROSroPTCAL TMAOERY. 



of gorgeous rings, rivalling each other in ])rismatic splendour, set 

 off by the sharp contrasts of jet black, well-defined borders, and 

 shaded with the most delicate tints, melting into one another with 

 an exquisite softness, reminded me of the eloquent and glowing 

 language of Sir John Herschell, when describing the phenomenon 

 of diffraction. Doubtless these appearances, emanating from the 

 solar orb, surpassed in intensity and brilliance those he examined. 

 Careful measurements gave the thickness of each coloured ring to 

 be i-i6,oooth,* the same as that of the central disc, whilst its black- 

 ring-setting was i-5o,ocoth thick. 



To subdue the intolerable brightness of the miniature sun, dis- 

 played on the microscopic stage, which was almost blinding in 

 brilliance, deeper eyepieces and a lengthened tube were employed, 

 till the whole field of views was entirely embraced by these magni- 

 ficent appearances. The observing objective was constructed for 

 a water film ; upon fixing a drop to the front, and securing it with 

 a fragment of cover glass, three-thousandths of an inch thick, I 

 was rewarded with the apparition of a solar disc, perfectly circular, 

 surrounded by a truly circular black ring (Figure 4). Each of these 

 splendid rings appeared of exactly the same breadth under t,ooo 

 diameters. 



The circular solar spectra formed by this J-inch piano convex 

 lens, viewed with a high quality immersion system, were thus 

 arranged, from the centre outwards : — 



Coloured Rings. Intervals. 



Ring I. —Solar disc, white ... Primary ring, jet black. 

 „ II. — Pale lavender ... Secondary ring, black. 



,, IV. — Lavender Third ring, ,, 



„ VI.— „ Fourth ring, 



„ VIII.— „ Fifth ring, 



,, X. — Pale rose Sixth ring, dark red. 



„ XII. — Bright green ... Seventh ring, „ 



„ XIV.— „ Eighth ring, „ 



„ XVI.— „ Ninth ring, 



„ XVIIL— „ Tenth ring, black 



„ XX. — Orange Eleventh ring, „ 



„ XXII. — Deep orange ... Twelfth ring, „ 

 „ XXIV- 



* Really 16K thousandths. 



