At the beginning of the seventeenth century there was at Lyons a very remarkable mansion built by a man named Nicholas Grollier de ServiÈre. This house was filled with all the most remarkable curiosities and inventions of the period. The owner belonged to an ancient family. His great-uncle, Jean Grollier, had amassed a magnificent library, the best in France. His father was also a celebrated adherent of Henry IV., and M. ServiÈre himself had inherited much scientific taste and intelligence from his ancestors. His house was full of curiosities, ingenious machines, and mysterious clocks, concerning some of which things we shall have something to say in this chapter.

M. de ServiÈre’s ingenuity was first apparent in the circular reading desk, or wheel-desk, on which he put all the books he was likely to require within a certain time. He seated himself by this revolving desk, and then was enabled to read any book or paper he desired by merely turning the wheel with his hands and thus bringing it under his vision. In these days it is equally possible to collect useful articles either of an electric nature or otherwise. We have already described the electric pen and the writing machine, with some other things which might be included in our list of domestic appliances, but the Chromograph has not been yet illustrated.

The Chromograph.

When we have written with a certain well-known violet “ink” upon a sheet of paper and applied it to a soft gelatinous surface and rubbed it a few times, we shall obtain an impression of the writing on the gelatine. By pressing blank sheets of paper upon this we may pull off quite a number of copies of our letter or circular. This practice is now so well known that it is scarcely necessary to detail it. The layer of gelatine is made up as follows, and any of the recipes will suffice.

1. Gelatine 100 grammes, water 375 grammes, glycerine 375 grammes, kaolin 50 grammes. (LebaigueÉ.)

2. Gelatine 100 grammes, dextrine 100 grammes, glycerine 1000 grammes, sulphate of baryta q.s. (W. Wartha.)

3. Gelatine 100 grammes, glycerine 1,200 grammes, bouillie de sulphate de baryta, strained, 500 cubic centimÈtres. (W. Wartha.)

4. Gelatine 1 gramme, glycerine À 30° 4 grammes, water 2 grammes. (Kwaysser and Husak.)

The “mixture” is shaken until it cools to the point of thickening, and then poured into a zinc vessel. The kaolin or the sulphate of baryta makes the composition white. It can be treated again with gelatine and molasses employed for printing rollers. When the proofs have been taken from the frame the surface may be rubbed with a damp sponge, and then it will be ready for use again immediately. The introduction of dextrine facilitates the cleansing of the surface plate.

The Campylometer.42

This instrument, constructed by Lieutenant Gaumet, is very easily carried in the pocket, and by a very simple process gives (1) the length of any line, straight or curved, traced on a map or plan; (2) the actual length corresponding to a “graphical” length on maps of the scale of 1/80000 or 1/100000, or on maps which are multiples of these numbers.

The instrument consists of a toothed disc, the circumference of which is dentated exactly in five centimÈtres. The faces of this disc each carry a system of divisions; one is divided into four parts, the other into five. The circumference of the disc (5 centimÈtres) corresponds to the 4 kilomÈtres of the scale of 1/80000, and to 5 kilomÈtres of that of 1/100000. The division 1/40 of the disc in the former scale measures 100 mÈtres, and is in it the same as 1/50 of the other scale.

The toothed disc moves upon a micro-metric screw, the markings of which are 0·0015 of a mÈtre, and a small “rule” or “reglet” carries equal graduations, as the screw representing lengths so follow:—

The micro-metric screw is fixed in a frame so made as to form a kind of indicator or guide at one side.

To make use of the campylometer, bring the zero of the disc opposite the zero of the rule (reglet), then place the instrument on the map in a perpendicular position; the point will serve as guide, and move the disc upon the line, whether direct or sinuous, of which you wish to ascertain the length.

When this has been done, note the last graduation of the “reglet” beyond which the disc has stopped, add to the value of this graduation the complementary length shown by the division of the disc which is opposite the “reglet.” To find the length of a material line we must add to the number of centimÈtres shown by the upper graduation the complement in millimÈtres furnished by the division to the 1/50th.

For example, suppose we read 20 upon the upper scale, 35 the division to the 1/50 opposite the “reglet”; the length obtained is 20 centimÈtres plus 35 millimÈtres, or 0·235 mÈtres. If we are measuring upon a map on the 1/100000 scale, the upper graduations represent kilomÈtres, the complementary divisions on the 1/50 scale hundredths of mÈtres.

For example, suppose again 20 be the superior graduation, 35 the division to the 1/50 of the disc as before; the distance measured is 20 kilomÈtres plus 3,500 mÈtres, or 23,500 mÈtres.

On the map the lower graduation of the “reglet” is used. For instance, if 12 be the upper graduation of the division to 1/40 of the distance opposite to the “reglet,” the distance measured will be 12,700 mÈtres.

The campylometer has been specially constructed for maps on the 1/80000 and 1/100000 scales, and calculations can be made easily for any maps whose scales are multiples or sub-multiples of these. But the instrument will serve equally well for all maps or plans of which the numerical scale is known. We must multiply the length of the line expressed in millimÈtres by the denominator of the scale divided by 1,000.

So upon an English map to the 1/63360, a length of 155 millimÈtres corresponds to a “natural” length of 63,360 multiplied by 155, or 9820·80 mÈtres.

Thus we perceive that the employment of the campylometer does not necessitate the tracing of a graphic scale, but only the knowledge of the numerical scale. When the former only is known, the campylometer may be used in the following manner:—

Having traced with the disc the line you wish to measure, carry the instrument to the zero of the scale and let it run inversely the length of that scale, until the zero of the disc returns opposite to the zero of the “reglet.” The point at which the disc is stopped on the scale indicates the length of the line measured upon the map. If the scale be smaller than the line measured, repeat the operation as many times as may be necessary.

If it is desirable to ascertain upon a map of a scale of 1/20000 the distance represented by 1,200 mÈtres, we have only to place the toothed disc so that its position marks four times the required distance—that is, 4,800 mÈtres on the map of 1/80000 (for 4 times 20 = 80). Then move the disc in the given direction until the zero returns opposite the zero of the “reglet”; this limit will mark the extremity of the length required.

Explanations are not easy upon paper, but the instrument is found very easy in actual use. It is employed by the military staff for calculating distances of any kind, curves or straight lines. On the march, or even on horseback, the campylometer can be employed.

Mysterious Clocks.

The clocks represented in the two following illustrations (figs. 878 and 879), are well worthy of being placed in the house of any amateur of science. They are made of transparent crystal, and though all mechanism is cleverly concealed they keep capital time. The former clock (fig. 878) is the invention of Robert Houdin, and consists of two crystal discs superposed and enclosed in the same frame. One carries the usual numerals, the other moves upon its centre with the minute hand attached, and its rotation induces by the ordinary method the movement of the hour hand. The requisite motion is transmitted to the dial by gear disposed along the circumference and hidden within the metallic frame, and is itself put in motion by clockwork, enclosed in the pedestal of the timepiece.

M. Cadot, in his clock (fig. 879), retains the plates, but adopts the rectangular form, so as to preclude all idea of rotation, and to puzzle those who are acquainted with the working of Houdin’s clock. The minute hand cannot, in this instance, be fixed to the second glass plate, it preserves its independence. This movable plate has only a very slight angular movement around its centre, which oscillation or “play” is permitted in the interior of the rectangular dial. A little spring movement, hidden in the central nut of the “hand,” provides in progressive rotation the oscillation of the transparent plate, which cannot be perceived to move.

To produce this “balance” motion the plate is supported upon a bar in the lower part of the metal frame. After the direct oscillation of which we have spoken, a little spring puts the machinery back. The direct displacement is produced by a vertical piston which raises the end of the bar. This piston rests upon a bent lever communicating with a wheel with thirty triangular teeth. Finally this wheel turns upon its axis once in an hour by a clockwork arrangement in the pedestal of the clock. Each tooth takes two minutes to pass, and the movement is communicated to the minute hand, which thus goes round the dial in the hour. The hour hand is controlled by a delicate arrangement hidden in the base. The illustration and notes will explain the working.

M. Henri Robert has also invented a very interesting clock, and one calculated to excite much curiosity (fig. 881).

We can see nothing but a crystal dial, perfectly transparent, upon the surface of which two “hands” move, as upon an ordinary clock face. There is no machinery visible, and electricity may be credited with the motive power, because the dial is suspended by two wires. But they will soon be perceived not to be connected with the hands, and all search for the mechanism will be fruitless.

The hands, moreover, turn backwards or forwards, and may be moved by a treacherous finger, but will always return as by a balanced motion to their position, not the hour which they were at, but to the time which it actually is. They will take their proper place notwithstanding all efforts to the contrary, and will then, if let alone, indicate the time as steadily as ever.

The hands of this very mysterious timepiece carry their own motive power, and consist of unequally balanced levers, so to speak, in which the clockwork arrangement is intended to disturb the equilibrium. This property is employed to indicate the hour and the minute, as we will attempt to show.

The minute hand is the balance, and it is very exactly poised. In the round box fitted to the end of this hand a plate of platinum is displaced by clockwork. The centre of gravity being displaced every instant by the revolution of the weight which goes round once in an hour, the minute hand is forced to follow, and carries the hour hand with it. By the hidden arrangements the hands are dependent one upon the other, but remain independent in movement. If they be moved backwards or forwards they will return automatically to their respective places, and if turned quickly round the minute hand will return to the proper minute, and the hour hand to the hour.

The mechanism is simple and ingenious; the principle, however, is not absolutely novel, and before M. Robert applied it many attempts had been made to move indicators by the machinery they themselves contained. But M. Robert has succeeded in adapting the idea beneficially and usefully, giving it a practical as well as an elegant shape.

A New Calculating Dial.

The small instrument herewith illustrated (figs. 882 and 883) is very serviceable for calculators, and its size adapts it for the waistcoat pocket. It can be used to calculate by addition, subtraction, multiplication, and division. Logarithms can be found, and the powers and roots of numbers—even trigonometrical calculations may be made by its aid. We need not go into any details regarding the principle of the little “circle.” Such explanations are only wearying and unsatisfactory at best. The principle is, simply stated, the theorem that the logarithm of the product of two numbers is equal to the sum of their logs. The size of the dial will of course regulate the length of the calculation. The instrument depicted permits of calculation to three figures with exactitude. M. Boucher, the inventor, hopes to succeed in perfecting an instrument of small size which will combine all desiderata, and calculate to high powers.

The Pedometer.

We all know how useful it is to be able to calculate distances approximately when upon an excursion or walking tour, and much trouble is taken by many tourists to ascertain the number of miles they may have walked in a certain time. The rapid success which the Pedometer has gained is a testimony to the need it has adapted itself to fill.

The pedometer is much like an ordinary watch in appearance and size. We perceive a dial with figures and spaces to show the number of paces walked. The cut represents the mechanism, which is exceedingly simple.

In the fig. 884, B is a counter-poise at the extremity of a lever, which oscillates around an axis, A. A screw, V, serves to limit the extent of these oscillations, and a spring which acts upon the counter-poise holds the latter to the upper end. The apparatus is completed by a movement which counts the number of oscillations of the lever.

So much being understood, it will be presumed that if we give to the instrument an “up-and-down” movement, the spring which holds the counter-poise, B, being too weak to compensate the force of inertion of the latter, it gives way and presses against the screw, V. When the opposite movement takes place the counter-poise is at the end of its course, and so on. Thus during a walk each step produces an oscillation which the counter registers.

In the hands of a careful observer, such a pedometer is capable of registering exact results, and the number of paces being counted, a very good idea of the number of yards and miles passed over can be arrived at.