376 
Notes. 
would make themselves acquainted with the most recent disco- 
veries in microscopical optics. The other paper is by one of the 
Secretaries of the Royal Microscopical Society, and is entitled 
“ Notes on Aperture, Microscopical Vision, and the Value of 
Wide-angled Immersion Objectives.” Mr. Crisp’s objeCt is to 
collecft the scattered matter on the subjeCt, some of which is 
printed, but the greater part exists in letters written by Prof. Abbe 
to Mr. Crisp and others. Pending the publication of an ex- 
haustive treatise now preparing, these notes are of great value, 
especially as most erroneous opinions respecting both the aper- 
ture question and the whole theory of microscopical vision are 
widely disseminated ; and it is to be hoped that Mr. Crisp’s notes 
may be reprinted in a form accessible to those who do not see 
the Society’s Journal. The paper occupies between forty and 
fifty pages, and, like Prof, Abbe’s, could not be abridged. A num- 
ber of important experiments with the diffraction speClra are 
described, and the microscopist would do well to repeat and care- 
fully study them, as their bearing as to what is really seen through 
the microscope suggests the gravest doubts whether certain ob- 
jects, such as the markings of diatoms, have been seen at all. 
The results of tampering with these diffraction speCtra by stop- 
ping out some and using others, are remarkable, even to the total 
change in the appearance of an objeCt the nature of which is 
perfectly known, e.g., a series of ruled lines. Both their direc- 
tion and their apparent number are capable of being changed, 
according to the diffraction speCtra allowed to take part in the 
formation of their image. 
ERRATA. 
Page 273, line 23, for “suppositious ” read “ supposititious.” 
Page 303, line 3 from top, for “ personal ties ” read “ personalities ” ; line 13* 
for “ Reichert and Goethe ” read “ Reichert and Goette.” 
NOTICE. 
Several important books, awaiting notice, stand over from want of space. 
Mr. J. Hepburn Davidson’s article on “ Sham Employers” is delayed owing 
to the illness of the author, but will appear in our July issue. 
