lifo .Mechanics, Physics, a~d Chemistry.

the speed will then begin to increase; but lhe moment that this takes place~ the balls of the revolving pendulum will by their increased centri- fugal action recede further from the centre of motion, and raising up the clutch box, k, Mll push down the clutch box, o, so as to engage the wheel, m. The consequence will be, a speed transmitted thrc)ugh the spindle, r, to the wheel, x, as much greater than the speed of the water wheel, as the wheel, r/, is larger than the wheel, m. Bat the wheel, x, being free to move, independent of the water wheel shaft, and being driven in the same direction, will have a relative motion round that shat~ precisely equal to this ditt~rence of speed. For instance, should this dif ference be five revolutions per minute, the wheels, s s, will each make five revolutions per minute; which acting through the arrangement of parts already explained on the adjusting plates at d d, will communicate to them an outward motion~ tending to increase the width of the jet aper- tures, and this action will continue until the water wheel resumes its proper speed; when the lever and clutch boxes will return to their former position, until another change of resistance calls for a renewed action of the go- vernor.

Let it now be supposed ~hat the resistance taken off, has been again put upon the water wheel, and it will be seen that an action precisely similar to what has been already described will take place, but in a con- trary direction. The wheel, x, wilI then have a relative motion in a con- trary direction to the motion of the water wheel, and an action will conse- .quently be transmitted to the adjusting plates, to draw them inwards, and increase the width of the jet aperture.

Photography on Glass.*

Having lately had my attention drawn to the system of obtainingpho- tographic pictures on glass, I was led, by the simplicity of the process, to make some experiments upon it, in the course of which I have succeeded in still thrther simplifying it. As it is highly probable that many of your readers are interested in this, as well as other branches of photography, I subjoin a description of my modifications. I shall, however, in the first place give a sketch of the mode of operating ,xhieh I believe is generally adopted by amateurs as being the simplest, for the benefit of such of your readers as may be still unacquainted with this interesting and beautiful process. It is as follows :--Having precipitated an iodide of silver from a solution of its nitrate, by adding to it a solution of iodide of potassium till it is re-disolved. A little of this solution of iodide of silver is then to be added graduallyto co]lodion (a description of which is giver~ below,) and well shaken with it. After settling, this mixture is ready for use. Having procured a piece of plate-glass of the size required, pour over it some of the iodized collodion, allowing it to spread over the sur- face of the glass, so as to cover it completely; and then to flow off at one of the corners. After a little practice, this becomes very easy, and a fine even coating is obtained. The iodized plate is now to be immersed ia a solution of nitrate of silver, 30 grains to the ounce of water, till the

' From the Glasgow Practical Mechanic's Joumal~ December, 1851,

Photography on Glass. 12i

solution flows evenly over its surface, and it is then ready for the camera. After removal from the camera, the picture is developed by pouring over it some of the following mixture:--

Pyro-gal l ic acid, . ~t grs. Glacial acetic acid, . 1 drm. Watcr , ~ 1 oz.

When the picture is sufficiently developed, it is first washed with water~ and the sensitive coating is removed by means of a strong solution of hyposulphite of soda. It is then to be washed again with water, and when dry, a little thin varnish may be poured over it, to protect it from being robbed off.

I now come to describe the modifications which I have adopted, and which I find not onIy simpler, but productive of a better result than can be obtained by the process which I have described.

The first of these re]ates 1o the iodized collodion, and was suggested. by the idea, float it was unnecessary to add iodide of diver to the collodion, as the addition of iodide of polassium alcove, on immersion in the nitrate oL" silver, would form the required coating of iodide of silver upon the glass. On trial I tbund this to be the case.

A* this point it may be wall to make some remarks regarding the pre- paration of the collodion, which is of so nmch importance in this process. it is made, as is now generally known, fi'om gun cotton dissolved ia sulphuric ether. There is, however, considerab]e difference inthe mode .;f preparing the c~tton for this purposo. I lind the most eertain mode of ,)10taining very soluble cotton, is to make use of nitric acid. Equal bulks ,of sulphuric acid and nitre will be found to answer very well. Let the e.otton be immersed in this mixture, and well saturated ~'ith it for about ~even or eight minutes; then let it he taken out, and thoroughly.washed m water, and dried.

We now arrive at the iodizing process, which may be simply effected d & u s : ~ ] o ?)ure sulphurio ether add about :~th of its bulk of alcohol, then a little iodideofpotassium, and after this the prepared cotton; let these be well shaken together tbr some time, and then allowed to settle. FOtlr or ~ive grains of iodide to the ounce of ether will be found sufficient.

The admixture of alcohol to the eflmr seems to be necessary in preparing collodion for our present purpose, as it will be found, if pu~e ether be ,,mployed, that little or no coating will be formed on immersion in th~ nitrate of silver. It must, at the same time, be observed, on the other hand, that when too much alcohol is added, the coating will be too opaque, preventing the light i?om penetrating. Thus, little more ~tlaIt ~he surface of the sensitive coating being acted upon, it is impossible to oblain a bold picture. It is difficult, by description, to point out the depth of coating required, but a very little experience will be sufficient ~:o determine this. The object is to avoid the ektremes above mentioned, viz., the having little or no coating at all, and the havfng a coating too opaque.

From the digieulty I have experienced in always obtaining_pure ether, • - - " ~ e a - - • " " (there being often a eonslderabL quantity of alcohol already mixed with

it,) I have been obliged to adopt the following mode of preparing iodized collodion. To 1 oz of ether add 5 or 6 g,'s. ~0f iodide of potassiunb and

Vow. X~YIII .--Tu*m) S ~ I ~ s . ~ N o . 2 . - -FrqJnuARr, 1852. 11

122 J]fechanics, Physic6 and C~mislry.

shake them well together for some time; after settling, the iodized ether should be poured oft~ and some of the prepared cotton added to it till the proper consistency is attained. Now, prepare a solution of iodide of potassium in alcohol, and add this to the iodized (.ol]odion till the coating formed by immersion in the silver solution is considered suiIieiently deep. This should be of a milk-like appearance, but at the same time consider- ably transparent, tbr reasons be!bre given. By this means, I am enabled with ease, t6 modify 'my collodion so as to obtain any depth of coating I may desire; the only objcctio~ ~ttending' this ad~lleralion being, the having to pay the price of ether tbr so much alcohol, which every one kno\vs is considerably cheaper. Ny next modification is in the preparation of lhe developing mixture. It will be noticed that pyro-ga]lic acid is recom- mended tbr this pro'pose, the acetic add b~.;nc~ added to prevent the ps'ro- gallic frmn atlackin/ ~lle parts unafti.~cted by light. This, in comn~olt with most other acids, it eltbcts; hut I have never been able by its use to obtain a pure white. From this eircums'~anee, I was led to try the ellbcts of other acids, and found nitric acid to an:.,wer my purpose. A diNcnltf, however, arose in the nice adjustment required in the proportions of the two acids, which induced me to try another well known developing agent, sulphate of iro:b and lhe res~dt obtained in this way was q~ite satisfaetol 7. The proportions in this case seem to be of much less im- portance, so that, wi~h very little care, an excellent developing mixture may be obtained. I subjoin the proportions which I have used xYiih sueeess~--

St@hate of iron, 12 grs. Nilric acid, 1 or ~ drop:.;. Water, . 1 oz.

If, fi'om any ~:ariation in the strength of the nitric acid, the dark parts of the picture should he spoiled by the action of the sulphate~ the addition of a little more acid will be tbund to prevent the evil.

By means of the above moditlcations, I have obtained some excellent results; the whites of the picture being very pure, and of a fine metallic appearance, much resembling frosted silver. II. R.

Glasgow, ~'ovember, 1851.

t w o have before us some examples of our correspondent's productions, which possess an amount of brilliancy and boldness unknown in the ordinary Daguerreotype process. Few modern arts can be said to be in a state so essentially transitionary as Photography; but the introduction of glass seems to promise, in its results, to throw all previous inventions into the shade.--ED. P. M. JOURXA~.

: For tl~ Journal of the Franklin Institute.

'Trial Trip of the U. S: Steams/@ "Fulton." By 6V~ief Nngi~2eer, B. F. IStlERWOOD, ~). S. Wavy.

Most persons -a, ho feel interested in matters of steam navigation, will remember the old l). S. steamship Fulton, built about 14 years :ago at the Brooklyn Navy Yard, where she has lain since that time a perfect speci- men of an utter failure. She was constructed for a war sea steamer, with