542 PROCEEDINGS OF THE 



measured in the divisions of the eyepiece micrometer. To find 

 the size, take in the table on the M column the number repre- 

 senting the reading, and the number in that line vertically below 

 the reading in the line will be the size of the object in microns. 

 Example : 0*1 mm. of stage micrometer spans 28 divisions of the 

 eyepiece micrometer. M is then 28. An object measures 19 

 divisions of the eyepiece micrometer. O is then 19. Utilising 

 the table, the size will be found at once viz. 68 //,. Should the 

 measured division or unit of the stage micrometer be 001 mm., it 

 is only necessary to move the decimal-point one place to the left 

 in the final reading, which would give the result in the example 

 above as 6*8/x. Similarly, if the measured unit of the stage 

 micrometer had been 1 mm., then it would be necessary to place 

 a cipher after the figures given in the table ; so in the same 

 example the object would have been 680 jx., or 0*68 mm. When 

 the unit of the stage micrometer is 0*1 in., the decimal-point must 

 be moved three places to the left ; with a unit of 0*01 in., four 

 places; and with a unit of 0*001 in. five places to the left. In 

 the example above, the object would measure 0*068 in., 0*0068 in., 

 0*00068 in. respectively. The table is published by Messrs. H. F. 

 Angus & Co., 83, Wigmore Street, London, W., price 3d. 



The President said they were very greatly indebted to Mr. 

 Nelson for this table, and to Mr. Grundy for putting the matter 

 before them in the way he had done. For his own part he would 

 welcome anything which saved him from multiplication, and he 

 should imagine from what he had heard that this was a sort of 

 ready reckoner for the microscope, and would be extremely useful 

 to any one who had many measurements to make. He thought 

 he should find a great use for it in checking his own results by 

 comparison. 



Mr. Ainslie thought that the table promised to be extremely 

 useful to those who wished to make measurements of minute 

 objects. If, however, instead of 28 they happened to find 28*7 or 

 29*3 it would merely be necessary to alter the tube length so that 

 the stage micrometer below covered a certain value of the eyepiece 

 micrometer. 



In measuring diatoms the tube length must be adjusted, and 

 having determined that, they must be careful not to touch the 

 correction collar, as that would at once alter the power of the 

 objective. 



