OF MASSACHUSETTS. 131 



tained with the same results as if the water displacement had been 

 taken. By taking several hundred measurements of mdth and thick- 

 ness for scallops of the same height a table has been formulated, 

 giving the average width, thickness and cubic volume for every sized 

 scallop. Thus having given the height of any scallop, the cubic vol- 

 ume can be found and any gain in length transformed into gain in 

 volume. 



Measuring Instrument. — Tor speed, exactness and uniformity in 

 measuring large numbers of scallops it was necessary to have a suitable 

 measuring implement. (Fig. 105.) The instrument, designed for this 

 work by the writer, consists of an inverted triangle, formed by two 

 strips of metal welded together at the apex of the triangle, and joined at 

 the base by a short cross piece. The whole instrument is made of brass 

 except the braised joint, and can be made as light as desired, although 

 there is danger of a heavy blow rendering a light measurer inac- 

 curate. Several sizes were used in the work, the most convenient 

 having a base measuring 3 inches. On the sides of the triangle the 

 scale is marked in millimeters. The measure is scaled in a simple 

 manner by taking across the broad end a certain width in millimeters, 

 measuring the length of the instrument, and subdividing it into a cer- 

 tain number of equal parts, each corresponding to 1 millimeter. 

 This gives easier and more accurate readings as it is possible to read 

 to % of a millimeter with the same accuracy as to 1 millimeter on an 

 ordinary rule, each division on the triangle having actual measurement 

 of nearly 5 millimeters. When measuring, the triangle is held with the 

 base away from the body, and the object is brought down the nar- 

 rowing sides until it strikes, at which point the measurement is read. 



The value of the instrument arises from the rapidity with which 

 measurements can be made, as only one movement is required to record 

 the length of an object. Measurements could be made nearly twice 

 as fast as by using calipers, where two movements are required. A 

 proficient person can measure as high as 400 scallops per hour, three 

 measurements being taken for each scallop, or a total of 1,200. The 

 ordinary person can measure about 300 in the same time, or 5 scallops 

 per minute. This instrument can be used for measuring a variety of 

 objects, and students of variation, where rough measurements are alone 

 required, will find it of great convenience. 



Growth Experiments. — The growth experiments were carried on in 

 two ways: (1) by measurements at definite periods of the various sets 

 in the different waters of the Commonwealth; (2) by growth in pens 

 at Monomoy Point, Monument Beach, Marion and Chatham. 



In the first case the work chiefly consisted of measurements, taken 

 as described above, of a large number of scallops at each time, so as 

 to obtain a correct average. During the first year three measurements 

 of each scallop were made, until sufficient material was at hand to 



