out are more fully represented in figure 2, which is drawn of the actual dimensions proposed. It represents a vertical section through the plane of the seconds-axis A. This is made to project about half an inch through the front plate of the chronograph frame, and carries a spiral cam, a, and an arm, b. The cam acts upon the end of a lever (not shown in the cut) which, by a ratchet movement, causes the wheel L, near the right of the figure, to advance one step at the end of every second.

The type-wheel K, which indicates the seconds, is connected with L by a spring. This spring comes into action only when the hammer happens to be down on the face of K (in the act of printing an observation) at the same instant that the lever, dropping off from the end of the spiral a, is urging the wheel forward. Were it not for the intermediate wheel L and the connecting spring, a second might be lost in the indication of the type-wheel K on such an occasion. As it is, the wheel L will move on to its proper place, bending the spring a little, and as soon as the hammer rises K will also be carried forward by the spring.

A cam, M M, on the wheel L drives the minute-wheel N by a similar lever and ratchet; and the hour-wheel, if it is thought worth while to have one, is to be driven from the minute-wheel in the same way.

It would be better perhaps to relieve the arbor A from the work of driving the second and minute wheels, by using for the purpose a separate clock movement controlled magnetically by the standard clock, as proposed by Prof. Hough; but this would involve considerable additional expense.

The type-wheel tt is mounted upon its axis BB, in the prolongation of A, its bearings being ivory boxes, represented at h and h'. This type-wheel is made as light as possible; the vertical portion is of steel as thin as is consistent with strength, while the rim is a thin strip of copper soldered to the steel disc, and bearing in raised type the figures 00, 02, 04, 06, &c., up to 98. The copper strip may be made by the electrotype process from a leaden matrix in which the figures have been sunk at proper intervals by a common type punch.

As this rim would be hardly stiff enough to print from without some support, the bearing h is held to its place by a spring little more than strong enough to support the weight of the wheel; when the hammer descends to make an imprint this yields a little, and allows the rim of the wheel to come down upon the bed F.

The wheel it is adjustable upon its axis so that its zero can be made to come uppermost at the instant when the wheel K effects the change of the indicated second.

The type-wheels K and N are constructed in the same way, only their rims are made heavy enough to print without any support except that afforded by the disc of the wheel.

The arm ee is firmly secured to the left-hand extremity of the axis B, and carries at one end two pins (y) near each other,

HAMMER

forming a fork; at the other end it has a little projection (x). The arm ff is delicately pivoted at (x), and at the other extremity passing freely between the pins of the fork (y) carries the steel pin d. At the middle it is expanded into a ring, gg, through which the arbor B passes without touching : ff is made of soft iron, and the annular expansion at the middle thus serves for the armature of the electro-magnet whose action is to produce the desired result at the touch of the observer's key.

A light spring between e and ƒ solicits f to the left, and thus whenever the electro-magnet is not acting keeps the pin d in the position represented in fig. 2, engaged with the arm b. In this state of things the type-wheel it will be carried round continuously by A. Of course the arms e and ƒ must be as light as consistent with sufficient stiffness, and their weight must bal. ance in all parts of the revolution, and neither tend to accelerate or retard the motion of the type-wheel.

Close behind the arms e and ƒ is placed a stationary disc of metal, HH, having one hundred equidistant holes pierced in it in a circle, so situated that whenever the arm ƒ is drawn to the right by the magnet (thus disengaging the type-wheel from the train) the pin d will immediately enter one of these holes, stop the type-wheel, and hold it in place until the magnet ceases to act.

This magnet is peculiar in having for its core, instead of a solid rod, an iron tube, through which the axis B passes. Thus the pole of the magnet is always in the same position with reference to the armature gg, notwithstanding its revolution. As only one pole of the magnet acts upon the armature it is necessary to make the coils more powerful than ordinary.

For bringing the hammer down upon the paper and moving the paper along after each impression any one of many different plans might be used. Probably the best, leaving expense out of the account, would be to have the hammer raised by an independent train of wheelwork, which should be unlocked by an electro-magnet at the instant of observation, thus releasing the hammer, and allowing the wheel work after the blow to move far enough to raise the hammer again, and carry the paper forward.

Another more simple plan is to work the hammer directly by a powerful electro-magnet, to which the magnet Z should act as a relay that is, whenever the pin d touches the disc H it should establish a current which should bring down the hammer upon the paper; the hammer in rising after the blow carries the paper along one space.

Provision is also made for carrying the paper along several spaces at the will of the observer, so as to leave an interval between the record of different stars.

Although there are only fifty numbers on the type-wheel which prints the decimal of the second, the record is made to the nearest hundredth. There being one hundred holes in the

disc H, the type which indicates the decimal of the second may either come in line with that which gives the whole seconds, or half a space above it, thus: 25.18 or 25-18; the first would be read twenty-five and eighteen hundredths, the second twentyfive and nineteen hundredths.

It is not intended to secure precise coincidence of error between the clock and chronograph-merely coincidence of rate. This is obtained by controlling the pendulum of the spring-governor from the clock. The type-wheels can be set so as to indicate the nearest whole second; and then the exact difference between the clock error and the chronograph error can easily be found by making the clock record itself occasionally at the beginning of a minute.

The operation of the instrument is then as follows. When the observer touches his key, the magnet Z acts upon the armature, and withdraws the pin d from its engagement with b, causing it to plunge into one of the hundred holes in the disc H. The contact of d with H in its turn, by a magnet not shown in the cut, brings down the hammer upon the paper o o and forces it against the type, a piece of impression paper being interposed.

When the observer takes his finger from the key, d returns to its original position and will engage with b at its next revolu tion. The hammer also rises, and in rising carries the paper along one space in readiness for the next impression.

As yet the printing chronograph exists only as an idea, but it is hoped that the idea will soon be realized, and the machine put in operation at the Shattuck Observatory. The result of the experiment will form the subject of a future communication. Dartmouth College, April, 1866.

ART. XVIII.-Note on the geological position of Petroleum Reservoirs in Southern Kentucky and in Tennessee; by Prof. J. M. SAFFORD.

THE object of the following note is to point out briefly the geological position of the petroleum reservoirs in Southern Kentucky and in Tennessee, so far as they have been met with within the field of my observations. I hope, in a future article, to give a summary of all ascertained facts with reference to the mineral oils of this region.

The accompanying general section will serve to illustrate the topographical and geological features of the region under consideration. The line of section extends from the Cumberland mountain, or table-land, in Putnam county, Tennessee, through Overton county, in a direction a little west of north, to Burksville, Kentucky, and thence to Glasgow. The entire distance is

about seventy miles. The region traversed by this line is a plateau, from 800 to 1000 feet above the sea, out of the nearly horizontal strata of which the larger streams have eroded valleys from 300 to 500 feet deep.

The following are the formations represented in the section: 7. Coal-measures, 400 ft., edge of table-land.

6. Mountain Limestone,' about 550 ft. thick in Putnam county; mostly limestones.

5. Siliceous group; the "knobstones" of Kentucky. From 300 to 500 feet thick, including the Lithostrotion beds as its upper part.

4. Black slate, Devonian and Genesee, having a maximum thickness of about 60 feet.

3. Upper Silurian mostly or wholly, from 100 to 150 feet thick; mostly a series of limestones, some of which are impure, approaching fine sandstone or shale in character. The existence of these strata in the region of Glasgow is mainly inferred from the fact that they are seen in certain sections to the northeast and southwest of this point. They are, however, comparatively unimportant, and thin out southeastward and disappear.

2. Nashville group, Mr. Dana's Hudson period; blue fossiliferous limestones with some calcareous shales, 500 feet.

1. Trenton limestones, at the base of the section.

It may be remarked, in passing, that one of the most striking features of this section is the almost entire absence of the Upper Silurian and Devonian formations. In the Tennessee and Cumberland river portions, the Upper Silurian beds are wholly wanting, while the Devonian series is represented by nothing more than the thin Black Slate-a fact pointed out by me many years ago.

I have represented in the section the geological places of what we may call typical petroleum wells by the short heavy vertical lines. We will notice them in descending order.

1st. In the Mountain Limestone. The heavy line at a in the upper part of this formation indicates simply the geological level of the "Beaty oil well." Its geographical and topographical positions are very different. The well is located in Kentucky on the Big South Fork of Cumberland river, and near the Ten

'The awkward term subcarboniferous ought to be dropped. Silurian rocks are subcarboniferous.

AM. JOUR. SCI-SECOND SERIES, VOL. XLII, No. 124.-JULY, 1866.