MEASUREMENT OF ORGANISMS. 7 



ant may then be compared with the color wheel. By this 

 means also the total melanism or albinism, viridescence, etc., 

 may be measured. 



Marking-characters. The quantitative expression of 

 markings or color patterns will often call for the greatest 

 ingenuity of the naturalist. Only the most general rules can 

 here be laid down. Study the markings comparatively in a 

 large number of the individuals, reduce the pattern to its 

 simplest elements, and find the law of the qualitative variation 

 of these elements. The variation of the elements can usually 

 be treated under one of the preceding categories. Find in how 

 far the variation of the color pattern is due to the variation of 

 some number or other magnitude, and express the variation in 

 terms of that magnitude. Remember that it is rarely a ques- 

 tion whether the variation of the character can be expressed 

 quantitatively but rather what is the best method of express- 

 ing it quantitatively. 



Aids in Calculating. An indispensable aid in multi- 

 plying and dividing is a book of reckoning tables of which 

 Crelle's Rechnungstafeln (Berlin: Geo. Reimer) is the best. 

 This work enables us to get directly any product to 999 X 999 

 and indirectly, but with great rapidity, any higher product or 

 any quotient. 



The tables of Barlow (" Tables of Squares, Cubes, Square 

 Roots, Cube Roots, and Reciprocals of all Integer Numbers 

 up to 10,000") are like our Table X, but more extended. 



The tedious work of adding columns of numbers is greatly 

 simplified by the use of some one of the better adding ma- 

 chines. There are many forms ; of which the best are made 

 in the United States. The author has used the " Comp- 

 tometer" made by the Felt and Tarrent Manufacturing Co., 

 Chicago ($225), and found it perfectly satisfactory. This 

 machine is manipulated by touching keys, as in a typewriter, 

 but it does not print the numbers touched off. In this respect 

 it is inferior to the Burroughs Adding Machine of the Ameri- 

 can Arithometer Co., St. Louis, Mo., which costs $250 to $350, 

 or to the Standard Adding Machine, St. Louis ($185). 



For the multiplication and division of large numbers the 

 Baldwin Calculator is well spoken of (Science, xvn, 706). It 

 is sold by the Spectator Company, 95 William Street, New 

 York, price $250. The same firm is agent for Tate's Im- 



