88 NATURAL SCIENCE. August. 1896. 



tioned are so minute and so close together that the paper looks white, 

 then if the negative be placed over the paper so that the lines register, 

 the print, which is made in the usual way, appears as a photogram in 

 natural colours. Now for the application to printing. If an ordinary 

 half-tone block be made from the negative, then impressions from 

 this, printed in ordinary printing ink, on paper similarly ruled with 

 coloured lines, will produce a result similar to that of the photogram 

 in natural colours. If this account does not exaggerate the perfection 

 of the work, it is clear that before long we shall be able to reproduce 

 coloured illustrations in our scientific books of far higher quality than 

 any that have hitherto been attempted, and at a cost but slightly ex- 

 ceeding that of the ordinary half-tone process print. At present, 

 however, it seems to us that both photograms and process prints must 

 be very dull in colour, since by the very conditions of the process, 

 wnite itself must be two-thirds on the way to black. Moreover, 

 since in printing the photograms it is absolutely necessary for the 

 lines to register to within one-six-hundredth of an inch, we do not 

 see how the difficulties produced by slight contractions and expansions 

 of film and paper can be got over. 



American Entomology. 



We have received the third and fourth bulletins of the technical 

 entomological series issued by the U.S. Department of Agriculture. 

 The former is a revision by Mr. C. L. INIarlatt of the North American 

 sawflies of the sub-family Nematinae. In his classification of the 

 group Mr. Marlatt follows Fr. Konow, the old genus NemaUis being 

 split up into several genera. Many new forms are fully described and 

 several figured. These insects are most numerous in the Boreal and 

 Transition zones of North America, decreasing in the South. A 

 similar distribution is to be noted on our side of the Atlantic, for 

 while Sweden possesses 95 species and Scotland 70, Southern Italy 

 has only 12. The fourth bulletin comprises short papers by various 

 authors on injurious insects likely to be introduced into the United 

 States from Mexico and Japan. It appears that the entomologists 

 are watching the frontiers prepared to wage war on invaders. 



