RORIC FIGURES RORQUAL 429 inner surface of the outer case ; and engineers observe examples in which the near surfaces of parts of machines become visibly impressed the one on the other. Without doubt these are instances of mere transfer of material ; and a sort of printing, due to such transfer during long contact, is obviously the explanation of such cases as those of the images which picture framers find impressed on glass or paper with which a print has been long in contiguity. Photographic negatives or positives sometimes produce latent impressions on paper, or through it on sensitive surfaces with which they are laid away ; and a sensitized plate from which one picture had been apparently discharged, receiving a second, has had the two pictures then developed on the same field. These and similar phenomena must be explained on sim- ply chemical principles. Mr. C. A. Seely of New York has observed that a sheet of sensi- tive paper, having been enclosed between sev- eral folds of a printed circular, and left within a book, of course in the dark, for about a week, impressions became visible on both sides of the sheet, and the printing on both sides of two or more folds of the circular became su- perposed on the sensitive paper, that of more distant folds being sometimes the more dis- tinct, and usually not on their own, but on the opposite side of the sensitive sheet. Mr. Grove observed peculiar spots on some trout, and placing freshly caught fish with a serrated leaf on each side in the sun, found that, after a while, that on the sunned side had impressed its image on the skin of the fish, while that in the dark had not. Grove experimented also by placing paper with letters cut in it between glass plates, making these with sheets of tin foil into a Leyden apparatus, and electrifying for a few seconds with a Ruhmkorff coil ; he then breathed on the inner surfaces of the glass, and images of the letters appeared ; or by exposure to hydrofluoric acid, these were permanently etched. Pouring over a plate holding this latent image a film of iodized collodion, treating as for a photograph, and exposing to diffused daylight, another image, also insensible, was by the consequent action on light induced in the collodion film ; and this being dried, removed, and submitted to devel- oping agents, the insensible molecular change by which characters were impressed on the glass by electricity was finally rendered mani- fest by visibility of the image in the film. The number and variety of the ways known in which the luminous, actinic, and thermal rays, as well as electric perturbation and discharge, are capable of modifying the condition, and doubtless the molecular constitution of bodies, have been since the time of the announcements by Draper and Moser continually on the in- crease; until we are at length led to admit that many or all of these agents must modify molecularly all bodies subjected to their in- fluence, and in turn their subsequent beha- vior to many of the physical forces. (See FLUORESCENCE, PHOSPHORESCENCE, and PHO- TOGRAPHY.) Finally, it appears no longer ne- cessary, with Moser, to ascribe these actions to latent light ; nor with Herschel, to claim a peculiar heat or set of "parathermic rays." RORQUAL, the largest of the whale family, distinguished from the Greenland or right whale (balana mysticetus, Linn.) by the pres- ence of a dorsal fin, and by nearly parallel lon- gitudinal folds extending between the arches of the lower jaw, from the under lip along the chest and abdomen. The name rorqual is of Norwegian origin, meaning " whale with folds;" the genus was named lalcenoptera by Lacepede in 1804; the whalemen give to it the names of razorback and finback. There are no teeth, and the baleen or whalebone is very short. The largest species is the great northern rorqual (B. [physalus] hoops, Flem.), probably the most bulky and powerful of liv- ing animals. The head is about one fourth the length of the body, which is longer, more slender, and less cylindrical than in the right whale ; the blubber is much thinner, rarely exceeding 6 in., and usually yields less than Great Northern Eorqual ^Bklasnoptera Loops). 10 barrels of oil, on which account, and also because the baleen is of comparatively little value, whalemen do not often attack this bold, restless, and powerful inhabitant of the ocean. The head is so flat that the longest baleen plates seldom measure 4 ft. ; there are many hundred plates, becoming toward the side? mere bristles; the posterior arch of the pal- ate is large enough to admit a man, though the opening of the oasophagus would not allow anything larger than a cod to pass ; the sieve is coarser and the swallow larger than in the right whale, indicating a totally different kind of food, the rorqual devouring not only me- dusje and crustaceans, but immense numbers of herring, pilchards, salmon, haddock, and cod ; Desmoulins says that 600 good-sized cod, and a great quantity of pilchards, have been found in the stomach of a single individual. The longitudinal folds of the under surface
