370 Dr. Barr/s Account of the Discoveries of Keber 



the development of animal types from the early dawn of a living 

 world, appears to have been carried on in North America in 

 strict analogy with the development exhibited in the British 

 Isles ; and your just inference, that the scheme of development 

 in your Tabular View will be more acceptable to the American 

 geologists than any other scheme of arrangement of the British 

 rocks which has yet been published *." 



Before I conclude, 1 may remark, that if some pages of this 

 paper be controversial, they are brought forward with no petu- 

 lance, but with a truth-loving spirit, and in a conviction of their 

 importance. It is impossible that observers should agree during 

 the investigations of a continually advancing science ; and earnest 

 respectful discussions on unsettled points of nomenclature or 

 classification of facts, so far from being unfit for the considera- 

 tion of a body like the Geological Society, are, under proper 

 regulations, of all subjects perhaps the best fitted for their sober 

 discussion. To adopt a rule that would prevent the mooting of 

 controverted questions, would be most unjust to the cause of 

 scientific truth and scientific progress. It would virtually as- 

 sume, that whatever scheme was once published in its memoirs 

 must never afterwards be the subject of criticism or of change — 

 a principle which could not be followed out by any Society 

 without very soon being injurious to its honour, or fatal to its 

 existence. 



XL VII. Some account of the Discoveries of Keber on the 

 Porosity of Bodies ; with Confirmations, By Martin Barry, 

 M,D., F.R.S. 



[Concluded from p. 293.] 



1. Method of proceeding with Dry Objects, 



" ^' "WT^^^ ^ ^^® ^^^^ pencil I first carefully cleansed the 

 ▼ ▼ object to be examined, the scalpel to be used, the 

 glass on which the object to be examined was to lie, as well as the 

 covering-glass, removing all adherent dust, in order thus to pre- 

 vent any confounding with other particles ; then, holding the ob- 

 ject to be examined over the glass, I very gently scraped with the 

 scalpel upon its surface, spread out the minute scrapings (partly 

 fallen and partly hanging to the knife) ; which was done either 

 with fine needles, or, still better (in order to prevent a sticking 

 together of the scrapings), by tapping, or gentle strokes with 

 the blade of the knife upon the glass. I then examined them 

 without moistening, but with a covering of glass under the 

 aplanatic eye-piece of the compound microscope with 200 

 * Extract from a letter of Professor Hemy Rogers, of the United States. 



