is a liquid known as _orthotoluidine_, which possesses a beautiful red colour, does not mix with water, and which has exactly the same density as water when the temperature of both is 75° F. or 24° C. At this temperature, therefore, if orthotoluidine be run into water, spheres should be formed; and there is no reason why we should not be able to make one as large as a cricket-ball, or even larger. I take a flat-sided vessel for this experiment, in order that the appearance of the drop will not be distorted as it would be in a beaker, and pour into it water at 75° F. until it is about two-thirds full. I now take a pipette containing a 3 per cent. solution of common salt, and discharge it at the bottom of the water. Being heavier, the salt solution will remain below the water, and will serve as a resting-place for the drop. The orthotoluidine is contained in a vessel provided with a tap and wide stem, which is now inserted in the water so that the end of the stem is about 1 inch above the top of the salty layer. I now open the tap so as to allow the orthotoluidine to flow out gradually; and we then see the ball of liquid growing at the end of the stem (Fig. 5). By using a graduated vessel, we can read off the quantity of orthotoluidine which runs out, and thus measure the volume of the sphere formed. When the lower part reaches the layer of salt solution, we raise the delivery tube gently, and repeat this as needed during the growth of the sphere. We have now run out 100 cubic centimetres, or about one-sixth of a pint, and our sphere consequently has a diameter of 5¾ centimetres, or 2¼ inches. To set it free in the water we lift the delivery tube rapidly—and there is the sphere floating in the water (Fig. 6). We could have made it as much larger as we pleased, but the present sphere will serve all our requirements. [Illustration: __Fig._ 6.—The detached sphere floating under water._] [Illustration: __Fig._ 7.—The Centrifugoscope._]