bits to touch at the colliding point, the resulting fragments would be-driven forth in a plane perpendicular to the course of their common center of gravity. If the velocity from the impulse were thirty-two per cent, of that required for describing a circle, they would be constrained to move in ellipses varying in eccentricity between ·32 and ·1024; and about seven eighths of the known asteroids conform to this limitation in the form of their orbits. Had the motion of both planets been merely progressive and coincident with the ecliptic, the orbital inclination for the fragmentary group would vary from to about 19°, yet the range would pass many degrees beyond this limit through the influence of rotation in the great spheres in causing their matter to fly more rapidly into space in a polar direction in the early stage of the collision. Yet this rotational movement would prevent the eccentricities of the numerous orbits from assuming the proportions which might be expected if the line of motion of the colliding orbs did not pass through their centers as in the supposed case.
There is another clew to the cosmical history of the region between Mars and Jupiter. The orbits of Saturn's moons show a near conformity to geometrical progression, and, taking the common rates at 1·30756, the following table gives the empirical as compared with the actual distances in equatorial semi-diameters of the primary:
| Mimas | 3·3607 | 3·3607 |
| Encaladus | 4·3933 | 4·3125 |
| Tethys | 5·7483 | 5·3396 |
| Dione | 7·5182 | 6·8398 |
| Rhea | 9·8325 | 9·5528 |
| 12·8600 | ||
| 12·8600 | ||
| 16·8190 | ||
| Titan | 21·9972 | 22·1450 |
| Hyperion | 28·7690 | 26·7834 |
| 37·6250 | ||
| 49·2510 | ||
| Japetus | 64·3590 | 64·3590 |
It appears from this table that two consecutive satellites are missing in each of the chasms in the Saturnian family, and this evidence of their transformation into asteroids seems more reasonable on considering the disturbing influences of Titan and Japetus on their planetary neighbors. The array of the satellites near Saturn would also lead to the belief of more worlds than one near the sun, and the vain search for Vulcan would render more probable the existence of an asteroidal group within the orbit of Mercury.
Listening to the Pulse.—We take from the "Lancet" an account of a new instrument—the sphygmophone—invented by Dr. Richardson, of London, and which transmutes the movements of the arterial pulse into loud telephonic sounds. The needle of a Pond's sphygmograph is made to traverse a metal or carbon plate, which is connected with the zinc pole of a Leclanché cell. To the metal stem of the sphygmograph is then attached one terminal of a telephone, the other terminal being connected with the opposite pole of the battery. When the whole is ready the sphygmograph is brought into use as if a tracing were about to be taken, and when the pulsation of the needle from the pulse-strokes is secured, the needle, which previously was held back, is thrown over, so as to make its point just touch the metal or carbon plate, and to traverse the plate to and fro with each pulsation. In so moving, three sounds, one long and two short, are given out from the telephone, which sounds correspond with the first, second, and third events of sphygmographic reading. In fact, the pulse talks telephonically, and so loudly, that when two cells are used the sounds can be heard by a large audience.
The Audiometer.—"Audimeter," or "audiometer," is the name given to an instrument invented by Professor Hughes, with the aid of which a person's power of hearing sounds can be very accurately measured. It is formed of a small battery of one or two Leclanché cells, a new microphonic key, two fixed primary coils, a graduated insulated bar, to which at each end one of the fixed coils is attached, a secondary induction coil, which moves along the graduated bar, and a telephone, the terminals of which are connected with the terminals of the induction coil. The principle of the audiometer is based on the physical fact that when the battery is in action, and a current is passing through the two primary coils, the secondary coil on the bar becomes charged by induction whenever it is brought near to either of the primary coils; but, when it is brought to the precise
