156 Transactions of the 



above, may be taken as an approximate account of what I saw on 

 the Begeeria Nigro-maculata of Mclntire. 



The so-called beading was readily brought out with any power 

 above the half-inch. Immersion lenses gave more satisfactory views ; 

 and the very best effects being obtained by the immersion yVth of 

 Powell and Lealand, I selected this lens for preparing the photo- 

 graphs. The appearance sought was readily obtained by oblique 

 light thrown lengthwise upon the scale from the concave mirror, 

 whether the illumination was afforded by a coal-oil lamp or by the 

 sun ; but the best results were secured by using the achromatic con- 

 denser of Powell and Lealand, diaphragmed down so as to transmit 

 a pencil of small aperture, and obtaining obliquity by decentering 

 the condenser somewhat by means of the screw movements of the 

 secondary stage. Many other tricks of illumination were tried, but 

 the above gave, on the whole, results most nearly comparable with 

 Dr. Pigott's description. I found the so-called beading was best 

 shown when the cover correction was so arranged as to show the 

 exclamation marks most distinctly. If, then, the illumination was 

 managed for the best display of the upper beading, I found on many 

 of the scales that a slight depression of the objective, by means of 

 the fine adjustment, brought the lower beading into view, and with 

 a stUl further slight depression the notes of exclamation were seen. 

 By slowly raising the objective in the same manner, the pheno- 

 mena were reproduced in reverse order. On some of the scales, 

 however, which I suppose to be those which lie with their under- 

 surface towards the observer, as the objective was lowered the 

 exclamation points were first seen, then the two sets of beading, 

 one after the other. The colours of the beading appeared to me to 

 be alternately greenish and reddish (I should hardly choose the 

 word pink), according to the position of the fine adjustment. When 

 the upper rows of beading appeared reddish, the lower rows were 

 greenish, and. vice versa. The beading, however, at its very best, 

 always resembled the " rows of peas in a pod." I praise the eyes 

 of the lady. They ran into each other ; they appeared, rather, as 

 irregular ribbings, with alternate varicose swellings and constric- 

 tions, than as rows of such isolated spherules as are seen on so 

 many diatoms. In size they varied somewhat, but rows of five or 

 six seldom measured less than toAo oth, and often as much as Tj-^oth, 

 of an inch long. The colours were most brilhant and the approxi- 

 mation to the spherical form closest when the sunlight was used. 

 The handsomest results were obtained when the direct rays of the 

 sun were allowed to fall upon the mirror at such an angle that just 

 so much light should pass the condenser as the eye could bear with- 

 out being dazzled. On interpolating in the solar pencil a cell con- 

 taining a solution of the ammonio-sulphate of copper, the definition 

 was materially improved, but the varicose ribs looked now even less 



