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secured it from danger of being scratched by contact with a slide passed over it. 

 In using the ordinary form of paraboloid, a great portion of the light was 

 totally reflected by the slide, upon the stop, causing a partial illumination of the 

 field, which appeared of a neutral tint instead of black ; but by the use of the 

 new paraboloid, this reflection was entirely prevented, and the object received ' 

 a much greater degree of light than it could in the ordinary way. The curves 

 of this paraboloid were worked up for a particular thickness of glass ; and if 

 the slide to be examined differed from this, it must be padded up with pieces 

 of thin covering glass in the same way as proposed by Mr. Wenham. One of 

 Moller's diatom slides, mounted in balsam, was exhibited in the room with 

 one of these new paraboloids for the inspection of the members. 



Mr. Hailes inquired in what respect, and why, the curves of this paraboloid 

 had been altered ? 



Mr. Ackland (from whose formula the paraboloid had been constructed), 

 replied that the object of the alteration was to avoid the reflection of light 

 from the under surface of the slide. The upper surface of the paraboloid was 

 very slightly concave, being on a radius of SO inches ; but the construction was 

 very different. 



A vote of thanks was unanimously passed to Mr. Jackson for his communica- 

 tion. 



Mr. James Smith exhibited to the meeting a simple contrivance designed to 

 obviate a difficulty frequently met with in using Ross's 4 in. objective, in con- 

 sequence of the great length of focus required. It consisted of a small mahogany 

 sub-stage, attached to the wooden stand of the microscope, and jointed so that 

 it could be set at any angle required to make it parallel with the ordinary stage 

 when the body of the instrument was inclined. The object to be examined was 

 placed upon the sub-stage, and viewed through the orifice in the upper stage, 

 by which means an ample length of focus and a great degree of steadiness were 

 obtained. For the illumination of opaque objects in this position, the concave 

 mirror was admirably adapted, and the lamp did not, in that case, require to be 

 placed so near to the instrument as to cause any inconvenient amount of heat to 

 the observer. The habits of living insects could be most advantageously studied 

 by this arrangement ; and he had recently observed, when examining a spider, 

 that, in attacking a fly, and enveloping it in a quantity of web previously to 

 finishing his meal, a silken thread was spun from each of the five spinnarets, 

 instead of from one only, as under ordinary circumstances. 



In reply to a question from Mr. Curties, 



Mr. Smith said he had not yet made any provision for examining objects by 

 reflected light ; but he intended shortly to give his attention to this, and thought 

 that it might be accomplished very easily. 



Mr. T. Crook suggested that a piece of plain looking-glass placed upon the 

 wood stand would answer the purpose. 



Mr. Golding thought that the small round looking-glasses sold at toy shops 

 for a few pence were all that could be required. 



Mr. Smith said that, although he had contrived this arrangement, especially 

 for a 4in. objective, it would answer equally well for a 3in., or even for a 2in. 



Mr. E. Richards thought it would be a great addition to the arrangement if 

 the front lens of the objective were made to draw out. He also suggested that 

 Reade's prism would answer very well for the illumination. 



The President said he would offer one more suggestion in addition to those 

 already made. Would it not be possible to arrange the instrument in this way 



