6l2 



SCIENTIFIC NEWS. 



[Dec. 14, 1E8 . 



provide for it in churches and halls. He was of opinion, 

 however, that that quantity was far more than was neces- 

 sary with any reasonably effective ventilation. He then 

 stated the principles to be followed to ensure the proper 

 ventilation of a room, and referred to the plan adopted 

 in schools and other buildings of introducing fresh air 

 all round the room, about six or eight feet up, and letting 

 the foul air out at an opening near the floor, as an entirely 

 erroneous principle,- and one which ought to be con- 

 demned. It seemed to him that to secure a perfect 

 system of ventilation the fresh air should be introduced 

 as near the floor as possible, through as short a channel 

 as possible, and should strike against some obstacle so 

 as to break up the current. The obstacle should be a 

 heating agent of some kind, as in our climate it was 

 absolutely impossible to have effective ventilation at all 

 seasons without means of heating the incoming air. The 

 object of his paper was not to discuss the relative 

 merits of the various systems, but if the principles were 

 understood the details might be varied in any way to 

 suit local peculiarities. 



FLINTS.* 



PROFESSOR JUDD said that in the previous 

 lectures they had studied the facts which were 

 taught them concerning flints— first by means of experi- 

 ments, and they had seen that by such experiments they 

 learned first the chemical constitution 01 flint, and 

 secondly the physical properties presented by the sub- 

 stance ; and in the second place they had tried to learn 

 what was taught them concerning flints by observation, 

 especially as to the mode of occurrence of this 

 substance. That night he proposed that they should 

 consider what the microscope taught them concerning 

 flints. He must point out at the outset that the micro- 

 scope was not, as many persons imagined, simply a toy 

 to be played with, and that everybody who bought a 

 microscope was of necessity a microscopist. Nobody 

 going to a shop and buying a violin fancies he thereby 

 becomes a violinist, even though the violin happens 

 to be a Stradavarius, or other exceptionally good 

 instrument. But somehow it had come to be thought that 

 all that it is necessary for a man to be a microscopist is to 

 buy a microscope, and if he buys a very expensive and a 

 good one he is necessarily a very good microscopist. 

 Such, however, was not the case. The results obtained 

 by the aid of the microscope depend to a certain extent 

 on the instrument, more could be done with a goodi in- 

 strument than with a bad one ; but much more depended 

 upon the eye that was placed behind the instrument, and 

 still more on what happened to lie behind the eye. A 

 good microscopist would do a great deal more with a bad 

 microscope than a man who had not studied the use of 

 the instrument at all would with the best instrument 

 that was ever fashioned. That night he would only 

 just call their attention to the nature of the instrument 

 he was going to endeavour to employ that evening. The 

 microscope he was now speaking of — the compound 

 microscope, which was the form of instrument with 

 which most of the important researches were made — 

 consisted of a number of pieces of apparatus joined to- 

 gether, but he would only call attention to the essential 

 parts. First, there were some lenses called the objective, 

 or the object-glass, and upon the nature of those lenses 



* Fourth Lecture to Working Men at the Royal School ot Mine*. 



the degree of magnification depended. There were ob- 

 jectives which would magnify only ten, or fifteen, or 

 twenty times with the ordinary eye-piece, and others 

 which would magnify many thousands of times. 

 At the other end of the instrument they had another 

 arrangement of lenses, constituting the eye-piece of the 

 instrument. Now, attached to that particular instrument 

 they had two other portions, which constituted the 

 apparatus he had already spoken of as the polariscope. 

 He had called their attention to the fact that they had 

 two boxes, one below, and the other above the instru- 

 ment, containing two transparent prisms of Iceland 

 spar which polarised the light ; and he had shown them 

 that although there was nothing but a transparent body 

 between the eye and the light of the. microscope, yet 

 when those prisms were turned in a particular position 

 no light passed through unless a crystallised substance 

 was placed upon the stage of the microscope, in which 

 case they got coloured light, which varied with the nature 

 of the crystallised substance used. Now, having called 

 those facts to their remembrance, he would point out 

 that they had a microscope arranged in a somewhat 

 different form from the microscope which was upon the 

 table, which could only be used by one person at a time. 

 If he wished to study flints for himself he should not askfor 

 a better instrument than that on the table,but unfortunately 

 he could only use it himself or ask others to come round 

 one at a time to use it. In order to get over that diffi- 

 culty he would endeavour to throw pictures of what was 

 seen under a microscope on to a screen. The way to 

 throw those pictures on a screen was to get an exceed- 

 ingly powerful light, and to pass that light through the 

 objective, and by means of lenses in front of the 

 eye-piece, to form images on the screen. The great 

 difficulty, however, was that this objective, especially if 

 it magnified greatly, was ot very small diameter, and 

 the light used must go through a very minute aperture, 

 and it was afterwards spread out by the lens on to a 

 large surface. Now, in order to get sufficient light to 

 show objects in a room of that size it was necessary to 

 have a most powerful light, and for that purpose he used 

 the form of electric light, which gave them very good 

 results. It was worked, like the electric lights used for 

 illuminating the adjoining museum, from a dynamo. 

 Everything depended upon the light being suffi- 

 ciently bright to retain a sufficient light when spread 

 over a very considerable area. He had hoped he should 

 be able to show them some things with tolerably high 

 powers ; but unfortunately the instrument had gone back 

 to the maker, and he had retained it until the last moment, 

 and even now he had sent it back without making those 

 alterations which were specially demanded. He would, 

 however, he hoped, be able to show them a sufficient 

 number of objects with a moderate power, a power of 

 magnifying something like thirty-five times or forty 

 times ; that was, every object would be magnified, as 

 seen in the first instance, thirty or forty times their 

 length and breadth. He hoped they would be able to see 

 most of the points that he had called their attention to. 

 Now, the question might arise, how should they examine 

 flint with the microscope ? If he put flint under the 

 microscope they would see very little of it. Flint, how- 

 ever, was a translucent object, and if they took a hammer 

 and struck it they might get off flakes so thin that light 

 would pass through them. Moreover he had pointed 

 out to them that flints, like some other forms of silica, 

 could absorb liquids, and if it was placed in oil they 



