basin. The pits were filled in solid with concrete, up to the level of 17 feet below high-water, the face being protected by two feet thick of Kentish rag as usual. Brick arches were then turned from pier to pier, to support the upper half of the wall, which was of the ordinary character.

To prevent the ground between the piers from falling through into the basin, vertical brick arches, 3 feet thick, were turned from counterfort to counterfort, and backed with puddle or concrete. These arches were founded in the clay, on the top of a strong slope of concrete, faced with a foot of puddle, to protect the surface from the water. The wall carried at the back of it a culvert four feet in diameter, for keeping up the water level in the Eastern Dock or the New Basin if required.

After the counterforts were finished, and the arches turned, the ground in front of the coping line was excavated, and the toes of the slopes and piers put in with Portland cement concrete, in the proportion of 1 of cement to 9 of gravel. This sets faster than lias concrete, and is heavier, a cubic foot of each weighing 139 lbs. and 129 lbs. respectively.

Before the water was let into the basin, the north wall resembled a massive viaduct more than a quay wall for ships to lie against; but after the water was admitted the arches were not seen, as their crowns were eight feet below highwater level.

The use of concrete by Mr Rendel in the London Dock extension is an excellent example of what good engineering ought always to be; viz., the application, in the best and most economical form, of the material closest at hand, so long as that is consistent with strength and durability.

Description of an Improved Induction-coil Machine. By WILLIAM HART, F.R.S.S.A., Philosophical Instrument Maker, Edinburgh.*

About twelve months ago I had the pleasure of showing you one of Ruhmkorff's induction coils, and a number of experiments in connection with it. Since that time I have very much improved its construction, increasing greatly the volume of the discharge, and rendering it capable of throwing sparks several times the length of any of the coils constructed by M. Ruhmkorff, and also reducing the number of the cells of the battery. I therefore thought that a brief description of the machine as it is now made by me, and the results obtained, might be interesting to the Fellows of the Society. The instrument consists of a bobbin mounted on a mahogany basement, inside of which is placed a condenser of alternate sheets of varnished paper and tinfoil. and tinfoil. The iron core (or bundle of iron wires) which forms the centre of the bobbin, is surrounded by a copper wire, which should be of sufficient size to carry freely the whole of the battery current, and of sufficient quantity to saturate thoroughly the iron core with magnetism. For this purpose I use three layers of one continuous length of No. 14 copper wire covered with cotton. Surrounding this primary coil is the secondary wire, which should be very fine, not larger than No. 35, covered with silk, and must be laid on perfectly even. It is insulated from the primary coil, and also from the layers next to it, by the thinnest gutta percha, which I believe to be the best insulating medium. The greatest care must be taken in protecting the ends of the layers, so as to prevent the sparks passing from one to the other. Ruhmkorff insulates his secondary wire with shellac ; but this substance, though an excellent insulator, is liable to crack. It is therefore better to use the gutta percha tissue; and by employing four or five layers between each layer of wire, perfect insulation will be secured. The two ends of the

* Read before the Society, and Instrument exhibited, 14th January 1861.

secondary coil, which are of thicker wire, are brought through the end of the bobbin and carried to the insulated pillars, and the discharges pass between points or balls, as the current is conducted by wires to other apparatus to show its effects. The current from the battery is received through the binding screws fixed on the springs on each side of the interrupter, by which it can be turned off and on, and reversed at pleasure. The hammer of the contact-breaker is made to vibrate freely between the iron core and the brass screw, terminating with a platina point at the back of the hammer. The power of the spring can be adjusted by the screw half way up the spring, by making it press the two platina points together, so that it will take a greater amount of magnetism to separate them. By this means the power of the machine can be regulated to the purposes required. The power of this instrument is immensely greater than that of the electrical machine. The discharge may be made so rapidly as to appear a continuous flow, and with a quantity so great, that a Leyden jar can be charged and discharged as rapidly as the ear can distinguish sounds, and with almost deafening effect. This instrument is not affected by the state of the atmosphere like the frictional electrical machine, and nearly all the effects of static or frictional electricity are produced by it, so that the position it is taking in this electrical age is one of considerable importance. It occupies a small space and is worked without labour. As the spring brake is self-acting, the battery used may be Grove's or Bunsen's, and for the most of the experiments two or three cells are sufficient; but for finer effects, through long tubes and large jars, six or eight cells should be used. This instrument can be employed with nearly all the apparatus used with frictional electrical machines, exhibiting the effects of electricity in motion with a power and brilliancy far exceeding that produced by the largest of them.

Supplementary Remarks on German Yeast, &c. By JOHN MACKAY, F.R. S. S. A., Pharmaceutical Chemist, Edinburgh.*

Nearly twelve months ago I had the honour to read a paper before this Society "On Bread-making, with a special reference to German Yeast." The general tenor of these remarks, particularly regarding the latter part of my subject, was of such a character as might have led not unreasonably to the expectation that, ere this time, plentiful supplies of the article then under consideration would have been prepared in this city, and sold for the general purposes of trade. I have therefore thought it might not be without interest were I to lay before you, in the form of a supplementary paper, more information regarding the preparation of German yeast; and at the same time give to the Society such particulars as will satisfy those present that the non-production of solid yeast in this country, does not arise from any want of success in my process or manipulation, but is really dependent on other causes, entirely apart from this, and which have still to be met, and if possible overcome. Should the following remarks be considered uninteresting to any now hearing me, they will have this recommendation, that they may be depended upon as the results of actual experience and practical observation.

I may here premise, that the value and estimation of German yeast have in no way diminished during the bygone year. Average importations from Holland and Germany have continued steadily to arrive; while into the port of London alone, the printed weekly returns show the receipt of several hundred baskets from Rotterdam. The large and continued demand, as well as the general use of this article, are still closely confined to England; but I have reasons for believing that bakers, confectioners, and even private families, in many districts throughout Scotland where it has been hitherto unknown, will yet avail themselves of this excellent ferment, and whenever the manufacture has been fairly established, become regular and steady consumers. It may be here men

* Read before the Society, February 11, 1861.

See paper printed in the Transactions, vol. v. p. 230.

tioned, that not only is this substance used regularly in Her Majesty's household, but so fond has the Queen become of bread baked with German yeast, that during her stay at Balmoral, there were supplies sent regularly twice a-week for the purpose of making bread and rolls for the royal table; while, to put the matter beyond all doubt, the following is a verbatim copy of a testimonial which was obtained some years ago from Windsor Castle, regarding the use of this foreign material. It bears date June 1853, and is as follows:-"We, bakers in Her Majesty's household, certify, that the dried German yeast is not only at present, but has been for more than twelve years, in constant use in Her Majesty's household, in fancy bread, rolls, buns, and all sorts of cakes, for Her Majesty's own table; and, further, do assert that there is nothing to equal the article for any of the aforesaid purposes.

(Signed) “J. HERMANN and N. C. SCHAFER."

With these few preliminary observations, I will now refer especially to the manufacture of this substance, which has for so long been a favourite on the other side of the Tweed.

Pursuing the investigations with which I had been previously engaged, I came to the conclusion that German yeast, as imported, was the yeast plant in a state of combination with some portions of the farina of the different grains with which it had been incorporated during the fermentation of the wort or infused seeds. This being my conviction, the peculiarities to be discovered and considered were,

1. The true source from whence to obtain the rough material.

2. The time or state when such material could be made most effectively available.

3. The most perfect mode of manufacture, so that its original virtues might be retained unimpaired; and,

4. The best way of preserving and keeping this article fresh and in good condition.

I propose very shortly to consider these different points separately, and in the order just noticed. The first will be quickly settled. Some years ago, as I have already stated in my former paper, I tried to manufacture German yeast from

VOL. VI.

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