branching canals, burrowed in the monadigerous mass, but the great circulatory apartment.

Spongilla arachnoidea Jas-Cl.

DESCRIPTION OF FIGURES OF PLATE II.

The following letters apply to identical parts in all of the figures. a, Inve membrane; outer division.-a1, Sectional profile of the cytoblastema of a— Cells in the thickness of a.--b', Cells (like those at b) about the spicules (Cells of the investing membrane, with their nucleus; a surface view.-. Ic porary junction (by contact only) of the outer (a) and inner (c) divisions of investing membrane.-c. Investing membrane; epithelioid inner division, i = tional profile.c1, Interspaces between monad-chambers.-d, Junction of the in sions of the investing membrane along the spicules.-e, Larger spiculesSmaller spicules.-f, Circulatory apartment.-g, Monadigerous mass., M chambers and monad groups.-i, Aperture of h.-j, Monads, or the body pr in figs. 3 and 3a.-k, Cylindrical collar of j.—l, Flagellum.-n, Nucleus.-os, Me” ostioles. v. Contractile vesicles.

Fig. 1. Magnified 320 diameters. Part of a very young Spongilla, of an oblas spheroidal form, and about of an inch in diameter. On the right is presents a face view of the investing membrane and the underlying monadigerous m On the left the focus is so adapted as to be fixed on a face-view of the monai-mas and at the same time on a sectional profile of the investing membrane at a, b, and d.

Fig. 2. Magnified 780 diameters. Interior of a monad-chamber, seen thro the aperture; the monads appear in end view, and crowded together side by sid like a pavement work.

Fig. 3. Magnified 1,600 diameters. A single monad, as seen in profile in the monad-chamber. Only two contractile vesicles were present in this specimen. The cylindrical collar (k) is extended to its utmost.

Fig. 3a. Magnified 1,600 diameters. Foreshortened, front view of a monad the body (j) in the distance; the hollow cylinder (k) projecting toward the ob server like a dark hoop, and the flagellum (1) in the center appearing as a black spot.

Fig. 4. Magnified 780 diameters. Sectional view of a monad-chamber, bringing the aperture (i) into profile, as well as the monads which lie at the same level; thus showing their convergence about the central open space.

ART. LV.-Description of a Printing Chronograph; by G. W. HOUGH, Director of the Dudley Observatory.

ABOUT the year 1848, the idea of recording astronomical. observations, by the use of galvanic electricity, was put in successful operation by different individuals. Since that time chronographs of various forms have been constructed for recording in a legible manner, on a moving sheet of paper, the time of any phenomenon observed. The great superiority, in point of accuracy and saving of labor, over the old eve and ear method, formerly used, led to the almost general adoption of the new plan.

During the past ten years the idea of constructing a chronograph, which should print with type the time of the observation, has been entertained by a number of persons. About five years since Prof. Hilgard of the Coast Survey, read a description

f an apparatus designed for this purpose, and about the same ime Prof. C. A. Young, of Dartmouth College, published a roposed plan for one,* But, so far as we are informed, the echanical construction of such an apparatus has not heretoore been attempted by any one.

The construction of a machine which shall carry a type heel, capable of giving impressions, with uniform velocity for number of hours together, without sensible variation in its notion, is a problem which is not easy of solution.

Some five or six years ago, in a paper read before the Albany nstitute, I gave an account of the method I proposed to adopt, nd in the construction of the machine, now to be described, e plan then proposed has been generally followed. My plan, hich is radically different from any other proposed, is based in the principle of using separate systems of mechanism for he fast-moving type wheel, and those recording the integer inutes and seconds, regulating each with electro-magnets ontrolled by the standard clock.

For a clear understanding of the mechanism, elaborate drawngs would be necessary. We shall, therefore, merely give a eneral account of its construction and peculiarities:

1st. A system of clock-work carrying a type wheel, with fty numbers on its rim, revolving once every second: one, vo, or parts of two numbers being always printed, so that undredths of seconds may be indicated. This train is priarily regulated to move uniformly by the Frauenhofer fricon balls, and secondarily by an electro-magnet acting on the st-moving type wheel, and controlled by the standard clock. his train is entirely independent, and can be stopped at pleasre, without intefering with the other type wheels.

2nd. A system of clock-work, consisting of two or more afts, carrying the type wheels indicating the minutes and econds. The motion of this train is also governed by an eleco-magnet, controlled by the standard clock, operating an espement, in a manner analogous to the action of an ordinary ock; every motion of the escapement advancing the type one umber.

There are three type wheels, indicating minutes, seconds and undredths of seconds. The integer seconds are advanced at very oscillation of the standard pendulum; and the minute, at e end of each complete revolution of the seconds wheel.

The type wheels are constructed of brass disks, around the rcumference of which is soldered a strip of electrotype copper, olding sixty numbers.

Presuming now we have this system of type wheels in operaon, it is necessary to print without disturbing their motion;

* See this Journal, No. 124, July, 1866.

especially is this true for the fast-moving type wheel. Afe long series of experiments, during which the fast me wheel was detached and stopped in various ways, we f made the impression from the spring of the hammer only allowing the blow to fall directly on the type, but arrestin about half an inch before it reached the top of the type. : this device, which is regarded of the greatest importance motion of the type is not disturbed an appreciable am Any number of impressions following each other in rapid s. cession, does not disturb the fast-moving wheel the one h dredth of a second. By this plan, none of the type wheels stopped or locked in the act of printing, and records of obser tions may follow each other as fast as the hammer can be to deliver the blow.

If the record is made while the type wheel indicating integ seconds is in the act of escaping, two numbers, or one num and part of another, is printed, so there is never any am uity about the record; this condition, of course, only occ when the fast moving wheel indicates 0-95 to 0·00s. If t numbers are printed when, for example, the hundredths real 98, the smaller of the integer seconds is the correct one. TE time required for the action of the escapement is about 0.06 se

The blow for printing may be struck directly, by means of strong electro-magnet; but the cost and trouble of keepin up a large battery for this purpose led us to do all the wor mechanically, only using electricity as the governing power Accordingly, a heavy running gear was built for raising the hammer, capable in its present form of delivering 2000 blows without rewinding; and it can be readily modified to give five times that number, if desirable. This gearing is entirely detached from the hammer when elevated, but is unlocked jus before the hammer reaches the type, immediately raising: again. The time consumed for this operation is about threetenths of a second, allowing, therefore, observations to follow each other at a minimum interval of one half second. When the hammer is elevated it is locked by an electro-magnet, the operation of this magnet allowing it to fall and print. The armature time of the hammer is about 0.07 sec., being but lit tle in excess of our ordinary chronographic recording pen; and since the hammer is acted on by gravity alone, the armature time will be sensibly uniform.

The types are inked by means of small rollers, covered with cloth, resting against their rim, and revolving with the wheel by friction. These rollers require inking every two or three days. If desirable, the inking rollers may be dispensed with, and impression paper used instead. After numerous experiments made with both methods, we have preferred the ink.

The paper fillet, two inches in width, is wound on a small pool, holding about 60 feet, and drawn between two rollers, he same as a Morse Register. Every time the hammer falls, he fillet is advanced about one-quarter of an inch, by the acon of an escapement driven by a weight. One spool of paper ill hold about 1200 observations, including the spacing for ifferent objects. This same escapement is also operated by an lectro-magnet, under the control of the observer, who, by ressing a key, is able to make spaces of any width between the rints.

The train carrying the minutes and integer seconds will run ight hours; the gear for elevating the hammer will deliver 000 blows; and the train for moving the paper fillet will go 200 times without winding. The fast moving train runs one our and thirty-six minutes; but since this train can be stopped t pleasure, without changing the zero of the type, its comparavely brief running is not a serious inconvenience. To recapitulate, we claim the following:

1st, Separate movements for the integer seconds and the undredths of seconds; 2nd, The method of regulating the undredths of seconds wheel by an electro-magnet in connecon with the standard clock; 3rd, The method of printing ouble or single numbers without stopping the type wheels; th, The method of striking the blow indirectly, using the oring of the hammer; 5th, The method of elevating and lockg the hammer. The minor details for paying off the paper llet, etc., may be accomplished in various ways.

The battery power required is about the same as for an ordiary chronograph. Three Grove elements, or six Hill's eleents, work the two electro-magnets well. A separate batof about the same size is used for the hammer and fillet agnets.

ry

In point of accuracy, this machine leaves nothing to be dered, and is much beyond what we thought possible. From a ast number of experiments, made by recording automatically he beats of the standard clock, both at the middle and end of he oscillation, the mean error for a single print is found to be pout 0·013 sec., equal in this respect to the recording chronoraph. The maximum difference in the records of the beats eldom exceeds 003 sec.; and we believe this is as much due the irregularity in the clock connection as in the running of le machine, since the same thing is found in ordinary chrono#raph records, where the measures are made from second to cond.

During the building of the machine, which was accomplished y my assistant, Mr. Foreman, and myself, the past winter, as e could find the time, a great many experiments were tried

AM. JOUR. SCI.-THIRD SERIES, VOL. II, No. 12.–DEC., 1871.

in the method of regulation, printing, etc. The fast moti, train was used to propel the integer seconds and minuter wheels, dispensing with the auxiliary movement; but the turbance of its motion was considerable, especially at the of every minute, when it had double duty to perform.

The saving of time and labor by the use of a printing chro graph is very considerable. At the lowest estimate, it de work equivalent to the labor of one person where three aree ployed at the same time. In our zone work in former yet when the zone extended two hours in right ascension, it usua required the labor of two persons a whole day to convert chronographic records into numbers and copy them on t blank forms. With the observations printed, this labor wholly dispensed with; since the "mean" is at once deduc from the printed records.

The machine is readily adjusted to indicate the same na bers as the clock's face, the type being so set as to print zerhundredths when the pendulum is at its lowest point, where th magnetic circuit is completed. In the construction of the appratus, provision was made for attaching engraved rings to the type wheel shaft, showing at a glance the time. But these are not found essential, as they would but little facilitate the setting of the type, which is accomplished as follows: The mit ute type wheel, which is free to move in either direction, revolved to correspond to the correct minute; an impression may then be taken, and the machine started, when the clock indicates the same; the seconds being readily counted from the beats of the magnet regulating the fast moving train. The whole time for this adjustment need never exceed two minutes.

In the observation of zone stars, the type may be set to give the integer-seconds of mean right ascension, so that the final reduction will always be a small quantity.

The constant use of this mechanism on every day and observ ing night, for more than four months, during which time more than ten-thousand records have been made, enables us to speak with confidence of its success, both as regards correctness in printing and in saving of labor.

Other things being equal, it is found, that for three observers twice as many observations can be reduced in the same time, as when a recording chronograph is employed.