28 THE STUDY OF SPEECH CURVES. 



using a pulley ten times the diameter of that on the motor the drum 

 speed becomes ^^^u of that of the motor. 



The tracing paper must be of a durable white color, not turning yellow 

 with exposure light. With the hinge recording point the glaze is not 

 needed to reduce friction; some of my records were made with specially 

 rough paper. This fact is readily explainable by the action of the 

 recording point; there is so little pressure that the glass point drags over 

 the smoke and not through it. Viewed under the microscope the point 

 is seen to drag flakes of smoke from the glazed paper. On some unglazed 

 paper it rolls the smoke up under it and then passes over the roll; on 

 this paper the curve is a series of dots. Such unglazed paper takes the 

 smoke evenly and makes a thinner line. Most rough papers, and some 

 glazed ones, too, seize the smoke so tightly that a clear tracing can not be 

 made. The long band of paper is pasted evenly at the joint; it should 

 run true when the drums are rapidly turned. 



The smoking may be done by an ordinary gas flame, provided it is 

 sufficiently rich in carbon. A tube with a series of holes making a set of 

 small flames is convenient; or a set of wax tapers may be used. Flames 

 that deposit sticky smoke are to be avoided. 



The best method to avoid jarring is to mount the apparatus on two 

 tables standing on a cement floor. When this can not be done, the tracing 

 portion may "be mounted on a platform or table suspended by ropes 

 and springs; the jarring of the floor is not transmitted to the apparatus; 

 the jarring of the ceiUng, however, may cause trouble. The method of 

 resting the platform on rubber cushions that may be blown up is suggested. 

 The far drum and the countershafts are placed on a table as far as space 

 permits from the tracing portion; the motor may be placed on this table 

 or on the floor. The motor should run with the minimum of jarring; if 

 necessary, it may be placed in a box of sand. 



The greater the distance between the two drums, the longer may 

 be the strip of paper and the less often the necessity of changing it; my 

 experience with distances up to 30 meters (100 feet) is that the longer 

 the strip the easier is the manipulation in every way. 



When a record is to be fixed, a solution of shellac is spread by a brush 

 on the back of the paper before it is removed from the drums; this fastens 

 the smoke from the back evenly to the paper and produces a dull surface. 

 Most glazed papers keep the varnish from coming through, but some 

 are perfectly porous. 



The apparatus must run slowly enough to avoid any swing from the 

 inertia of the lever when large curves are being registered. I have found 



