220 



SCIENTIFIC NEWS. 



[Mar. 9, li 



over it. That something is nol the ears of corn carried 

 from one side of the field to the other, but is the change 

 of colour due to your seeing the sides or lower ends of 

 the ears of corn instead of the tops. A laying down of 

 the stalk is the thing that travels in the wave passing 

 over the cornfield. The thing that travels in the wave 

 of water is an elevation of the water at the crest, and a 

 depression in the hollow." Dealing with the procession 

 of waves formed by a boat dragged along a canal. Sir 

 William alluded to the splendid researches made in 

 connection with that branch of the subject by Scott 

 Russell more than half a century before, which brought 

 about the discovery that this procession of waves in the 

 rear only occurs when the speed of the boat is less than 

 a certain limit. This discovery led to the Scottish 

 system of fly-boats, carrying passengers on the Glasgow 

 and Ardrossan Canal, and between Edinburgh on the 

 Forth and Clyde Canal, at speeds of from eight to thirteen 

 miles an hour, each boat drawn by a horse or pair of 

 horses gallopping along the bank. The method originated 

 from the accident of a spirited horse whose duty it was 

 to drag the boat along at a slow walking speed, taking 

 fright, and running oif, drawing the boat after him. It 

 was discovered that, when the speed exceeded the 

 velocity acquired by a body falling through a height 

 equal to half the depth of the canal, the foaming, stern 

 surge, which used to devastate the banks, ceased, and the 

 vessel was carried on through water comparatively 

 smooth, with a resistance greatly diminished. The 

 mercantile value of this fact was readily perceived and 

 taken advantage of. Special light boats, sixty feet long, 

 and six feet wide, were constructed of thin sheet iron, 

 and drawn by a pair of horses. The boat was started at 

 a slow velocity behind the wave, and at a given signal 

 it was by a sudden jerk of the horses drawn up on the 

 top of the wave, where it moved with diminished 

 resistance, at the rate of seven, eight, or nine miles an 

 hour. In illustration of this same principle Scott Russell 

 was quoted also as saying, " Two or three years ago it 

 happened that a large canal in England was closed 

 against general trade by want of water, drought having 

 reduced the depth from twelve to five feet. It was now 

 found that the motion of the light boats was rendered 

 more easy than before : the cause is obvious. The velocity 

 of the wave was so much reduced by the diminished 

 depth, that, instead of remaining behind the wave, the 

 vessels rode on the summit." 



Leaving canal waves, and turning to waves made by 

 ships in the open sea, Sir William paid eloquent testi- 

 mony to the valuable investigation made by Mr. William 

 Froude and his son, and said, that the whole pattern of 

 waves is comprised between two straight lines drawn 

 from the bow of the ship, and inclined to the wake on 

 its two sides at equal angles of 19° 28'. He then drew 

 attention to the wave-profile for certain ships, and 

 pointed out how from the appearance of the waves 

 raised by ships going at high speeds it may be learnt how 

 quickly they were going. After defining that the 

 " entrance " is that part of the ship forward where it 

 enters the water, and swells out to the full breadth of 

 the ship, and that the " run " is the after part, extending 

 from where the ship begins to narrow to the stern, the 

 lecturer explained the advantages and disadvantages of 

 a parallel middle body being introduced between the 

 entrance and run, and showed that it produced a good or 

 bad effect according to the relation of the wave length to 

 the length of the ship. When the effect of the entrance 



or bow, and the effect of the run or stern was such as 

 to annul, or partially to annul each other's influence in 

 the production of waves, then we had a favourable 

 speed for that particular size and shape of ship. On the 

 other hand, when the crest of a wave astern, due to the 

 action of the bow agreed with the crest of a wave astern 

 due to that of the stern, then we had an unfavourable 

 speed for that particular size of ship. 



In conclusion. Sir William suggested that in order to 

 get high speeds of eighteen and twenty knots an hour a 

 return should be made to the old French lines for 

 vessels. It was probable that by swelling out the ship 

 below in that old fashion, instead of having vertical 

 sides — making the breadth of beam say five feet more 

 below the water than at the water-line, a large addition 

 might be obtained to the displacement or carrying power 

 of the ship, with very little addition to the wave dis- 

 turbance and wave resistance. 



ELECTRIC PROJECTION MICROSCOPE. 



IN our climate the solar microscope cannot be de- 

 pended upon for exhibiting microscopic objects to a 

 class of students or at a lecture, and the lime-light, with 

 its cumbrous belongings and its risk of accidents, is not 

 all that might be desired. We are, therefore, glad to 

 have the opportunity of giving a description and illus- 

 tration of the electric projection microscope, devised by 

 Professor Selenka, of the Zoological Institute of the Uni- 

 versity of Erlangen. 



The stand (A) is of cast-iron, with a vertical support (B). 

 At a convenient height there is a board (C), on which 

 are laid the preparations, and above this board are 

 arranged two iron tubular pieces (D and E), the one above 

 the other, which receive a strong iron bearing-rod, and 

 can be fixed by means of the set-screws (Oj and O2). 

 The lower and shorter of these tubes supports on the 

 horizontal arm (F) the plate (G), with the condensers 

 (Hj and H»), as well as the table (J) with the microscope 

 (K). To the upper and longer tube ( E) is fixed the 

 light-chamber (L), with the arc lamp (M) screwed on 

 above. The arc lamp used is on the Piette-Krizik 

 system, which, in consequence of its easy and accurate 

 regulation, is especially suitable. 



The arc lamp (M) can be moved up and down, so that 

 the electric arc (X) can be adjusted to the optical axis 

 of the two condensers'' This adjustment is effected by 

 turning to the right or the left an iron disc (N), placed be- 

 tween D and E, and provided with an internal thread upon 

 the thread of D, so that, at the same time as D, the tube 

 (E), with the light-chamber (L) and the arc lamp (M), 

 moves up and down, and the luminous point (X) is set 

 higher or lower. A displacement of E with the light- 

 chamber is not possible, because the plate (G) — which 

 closes the light-chamber (L) in front, and carries the 

 condensers (Hj and H,) and the glass-trough (S) — runs 

 in grooves in the front edge of the light-chamber, so that 

 these parts can only move vertically. O is the object- 

 bearer ; P a rack-work ; Q an objective-revolver ; R a 

 screen, with an aperture one centimetre wide; and T 

 the micrometer screw. 



The light-chamber is made of strong oak, and to its lid is 

 screwed the arc lamp, from which hang down the two 

 iron rods supporting the carbons. In the lid of the light- 

 chamber there are, besides the aperture fur the carbons, 

 some ventilation-holes for the escape of the heat. These 



