Prof. J. C. Draper on an Improvement in Filtration, 335 



learned colleague remarks with reason that a multitude of recent 

 discoveries tend to render these limits obscure. Recent investi- 

 gations establish passages between the Devonian and the Carbo- 

 niferous. The Rhsetic stage has filled up a part of the hiatus 

 between the Trias and the Lias. The freshwater deposits lately 

 discovered by M. Matheron strengthen the bond between the 

 Cretaceous and Tertiary periods. The later Tertiaries can 

 hardly be distinguished from the older Quaternary. Why should 

 not the Tithonian stage in its turn diminish the value of the se- 

 paration between the most recent Jurassic and the Lower Cre- 

 taceous stages ? 



We think, therefore, that in this important question it is 

 more than ever desirable not to oppose to the facts which are 

 being collected nowadays a determination not to accept them, 

 founded upon a supposed impossibility. We must subordinate 

 the teachings of the schools to those of well-observed facts, and, 

 without choosing to throw ourselves with break-neck impetuo- 

 sity into the course of a revolution, we must remain impartial 

 in the investigation of the facts which will perhaps force us to 

 accept it. I will only add that prudence commands us to be 

 strict in their appreciation. 



XLVI. An Improvement in Filtration. By Prof. John C. 

 Draper, M.D., College of the City of New York*. 



TO those who have been unable to employ Bunsen's im- 

 provement in filtration because of an insufficient supply 

 of water to produce the necessary exhaustion, it may be of in- 

 terest to know that all the practical advantages may be obtained 

 by means of a simple and inexpensive apparatus, which it is the 

 object of this communication to describe. 



The apparatus consists of a stout boiler (a), with three open- 

 ings accommodating respectively a pressure-gauge (b), a supply- 

 funnel (c) for the introduction of water, and a tube (d) connect- 

 ing with the exhausting arrangement or steam vacuum-tube (e), 

 represented in section at/, in which /is a brass or glass tube 

 J an inch in diameter, terminating in a small conical opening or 

 nozzle 3^ of an inch in diameter. In the interior of/ and pass- 

 ing air-tight through the stuffing-box (h) there is a similar tube 

 (g) about I inch in diameter, and terminating in a nozzle or 

 opening like/, and about ^ of an inch in diameter. At £ a tube 

 J inch in diameter opens into / 



* Communicated by the Author. 



