288 NATURAL SCIENCE. April. 1896. 



But, though colour is all very well for demonstration purposes, and sometimes 

 for use in the field, it has many disadvantages. The darker colours obscure the 

 detail, so as to render it illegible, and in hand-painted maps the colour runs after a 

 wet day in the field. Maps are not always accurate, and it is difficult to alter a 

 coloured map. Again, it may happen that one wishes to colour on a different plan, 

 or for some different object, and yet to be able to have the geological lines visible in 

 the same sheet : this cannot be done in a coloured map. Therefore, it ought to be 

 possible for anyone to purchase plain one-inch maps with the geological boundary 

 lines engraved ; and on the inside of such boundary lines the designatory letters 



should be placed at sufficiently convenient intervals g5- gs- 



after the plan of contour-lines on the six-inch map. These maps could be produced 

 as cheaply as the present plain maps, and the student could get half-a-dozen of these 

 for the price of a coloured one. From my experience in the field I venture to say 

 that such maps are all the field-worker requires, and that coloured maps are a 

 plague to him. S. S. Buckman. 



[While sympathising with Mr. Buckman's request, we may point out that some 

 of the charges he brings, such as illegibility and running of colour, do not apply to 

 the new colour-printed maps. — Ed. Nat. Sci.] 



A Correction. 

 In your note on the University of Minnesota (vol. viii., p. 67), for ^iV-testing read 

 o;r-testing. This misprint is not your fault, but came, as you stated, from Science. 



Your review of Miss J. E. Tilden's " Bibliography of Algae " was objectionable. 

 You grumbled because it was incomplete. But it is entitled a Contribution to the 

 Bibliography, etc., and was avowedly incomplete. Further instalments will be pub- 

 lished, a large one being now almost ready. The intention is finally to correct it up 

 and issue on cards. 



I like Natural Science immensely. It is indispensable. — ^ Yours truly, 

 University of Minnesota, Conway MacMillan. 



January 21, 1896. Head Professor of Botany. 



"A Rowing Indicator." 



Mr. E. C. Atkinson desires to point out that on page 132, line 39, the words 

 " in cases 3 and 7 in excess or defect " should be " in some cases i or 2 in excess or 

 defect." The photograph reproduced in Fig. i was kindly taken by P. Elford, Esq., 

 St. John's College, Oxford. 



NOTICEJ. 



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 shoiM be sent in not later than the loth of the preceding month. 



To the Trade. — Natural Science is published on the 2^th of each 

 month ; all advertisements should be in the Publishers hands not later than the 

 20th. 



The " Challenger " Number. — In reply to enquiries, we remind our 

 readers that, although the First edition of this ran out of print immediately, 

 there are still some copies of the Second edition to he obtained at the usual price — 

 One Shilling. No more ti'ill now he printed, so orders should be sent at once. 



