SUPPLEMENT. 383 



216. Here I read : u If any one makes out new points of struc- 

 ture by any new method, all that such an authority who differs 

 has to do is to state that he has not been able to see the struc- 

 ture described so and so. Authority too often denies the ex- 

 istence of what it has itself been unable to see. Many auth- 

 orities deny the existence of what they haye not seen, while 

 they have not taken the pains to try the only method of demon- 

 stration by which the appearances in question could be seen." 

 Now we perceive that the Doctor is in a complaining mood. 

 The root of the matter was simply this : Dr. Beale paid great 

 attention to instrumentation ; the first l-25th and the first l-50th 

 objectives in existence were made for him ; he was not very par- 

 ticular as to their angle, although it is noticeable that he 

 claimed for them " plenty of light." But the fact is indisput- 

 able .that his instrumentation has been in advance of that of the 

 London microscopists. Dr. Beale was in fact in a position very 

 similar to those of the present day, who, conscious of the superi- 

 ority of their glasses, are disposed to regard the blind " authori- 

 ties " referred to as unworthy of special consideration. 



I desire in this connection to call your attention to the history 

 of the diatom of which we have all of us heard so much about 

 during the past nine years. I refer to Amphipleura pellucida. 

 Who of us here cannot recall the time when the existence of 

 striae on this shell was stoutly denied ? We can remember, too, 

 when Dr. Woodward settled this much vexed question by pro- 

 ducing his photographs displaying the striae on what he was 

 pleased to call " this well-marked diatom." And now that these 

 markings are no longer to be questioned, as exhibited on dry 

 mounts, and by the employment of monochromatic sunlight, 

 full eighty per cent, of our American observers fail to exhibit 

 41 this well-marked diatom" by lamp illumination, even when 

 dry mounted. I have a balsam mount of this shell with me, 

 and hope to show you the lines of No. 20 of the Holler plate 

 this eyening before we part, and also the 19th band of the 

 Nobert test plate, and by the aid of American made lenses of 

 medium power. 



Let me call your attention, for a few moments only, to another 

 .subject. We often hear the diatomist spoken of in terms, 



