August 22, 1884. J 



SCIENCE. 



149 



angles of the scrapers, raising their lips, and 

 preventing their cutting so deeply into the 

 mud. Better results were thus obtained ; but 



Fig. 6. — The Challenger's dredge. 

 {From ' The Atlantic:) 



far better ones followed the completion of the 

 flat frame, which was soon afterwards con- 

 structed, and used during the remainder of 

 the cruises. 



The Blake dredge, as it is called, was devised 

 by Commander Sigsbee, U.S.N., and Master 

 Jacoby, U.S.N. ; the "object sought in the 

 fashioning of the new dredge " having been, 

 according to the account of Mr. Sigsbee, " to 

 effect a skimming of the bottom rather than a 



deep penetration therein." Its essential fea- 

 tures (as shown in fig. 7) are its broad, non- 

 flaring scrapers, and rectangular iron frame or 

 'skeleton box' outlining its entire shape, the 

 entire framework being rigidl} 7 joined together. 

 These cause it to rest flat upon the bottom, and 

 prevent its digging in beyond a slight depth. 

 The small quantity of mud which enters at a 

 time is being constantly washed from the net, 

 to a greater or less extent, by the force of the 

 water passing through it, leaving only the 

 coarser portions and the specimens behind. 

 When a sample of the fine bottom-material is 

 desired, the lower part of the net is lined with 

 some open-mesh cloth, like muslin or scrim. 



The length of the 

 frame is about four 

 feet, the width about 

 three feet, and the 

 depth nine inches. 

 The scrapers are six 

 inches wide and three- 

 fourths of an inch 

 thick, being bevelled 

 on the inner faces at 

 the front to form sharp 

 edges. The net, con- 

 structed of twine web- 

 bing, hangs loosely 

 within the frame, over 

 which a canvas cov- 

 ering is fastened for 

 its protection . As 

 used by the Blake, a 

 transverse bar of wood 

 or iron, for the attach- 

 ment of weights and 

 tangles, was secured 

 to three sister - hooks 

 at the hinder end of 

 the frame. 



This form of dredge 

 has since been adopt- 

 ed by the fish-commis- 

 sion for deep-sea ex- 

 plorations, and often 

 replaces the simple 

 frame and net used in 

 connection with the 

 Chester rake - dredge 

 described below. 



Fig. 



— First form of the 

 Blake dredge. 

 {From Sigsbee'' s 'Deep-sea 

 sounding:) 



Rake-dredges. 

 In 1871 Prof. A. E. 

 Verrill, in immediate 



charge of the dredging operations of the U. S. 

 fish-commission, conceived the idea of supple- 

 menting the work of the common dredge bv the 



