38 



THE AMEEICAN MONTHLY 



[February, 



bridge, jr., before the Franklin Institute, 

 some striking statements were made con- 

 cerning the extremely minute size of the 

 ultimate molecules. The lecturer said : — 

 ' The gold-beater, as you doubtless know, 

 will hammer out the metal into leaves so 

 thin that more than 4,000 are required to 

 make a pile one millimetre in thickness. 

 But vastly thinner gold leaves may be 

 obtained in another way. By electro- 

 plating a known weight of gold upon one 

 side of a sheet of copper foil of given 

 dimensions, a coating of gold may be 

 obtained upon the copper whose thickness 

 is readily ascertainable by a simple cal- 

 culation ; then, by using a suital3le sol- 

 vent, the copper may be removed, when 

 the leaf of gold will remain intact. 



' After a series of careful experiments, 

 I have obtained, in this way, sheets of 

 gold, mounted on glass plates, which are 

 not more than ^5^0x1 of '^ millimetre thick; 

 and I have some specimens to show you 

 which I have good reason to believe are 

 not more than ^^oTjVoff of a millimetre. 

 To give you an idea of this thickness, or, 

 rather, thinness, I may say that it is about 

 T^^ part of a single wave-length of light. 



' Taking Sir William Thomson's esti- 

 mate of the size of the final molecules, 

 and considering that each layer corres- 

 ponds to one page of a book, our thinnest 

 film would then make a pamphlet having 

 more than a hundred pages.' 



— Among the many gorgeous objects 

 for the polariscope, the ethyl ether of 

 gallic acid, or ethyl gallate, first brought 

 to notice by Dr. Christopher Johnston (see 

 this Journal, vol. iv, p. 192), cannot be 

 surpassed by any crystals we have seen. 

 The finest crystals of this compound that 

 have come to our notice are those pre- 

 pared by Prof. W. H. Seaman, of this city, 

 who may have some preparations that he 

 would exchange for first-class mounts. 

 The method of preparing the compound 

 is described in this Journal, vol. v, p. 82_ 



— We would like to know for what 

 reason Dr. T. B. Redding, in the Physio- 

 Medical Journal, is abusing eminent 

 scientific gentlemen so unreasonably. 

 Really, we cannot see any good to come 

 of such articles as he has been writing 

 upon ' The Molecular Theory of Sound,' 

 and it is a great pity that so much ink and 

 paper should be wasted in such a manner. 

 To characterize a correct explanation of 

 physical phenomena as a ' fraud ' is not 

 very elegant, to say the least ; and as for 

 such specious language as we find in his 

 apparently interminable discussion of this 

 subject, it can only mislead the ignorant. 



Yet for that reason it should not be print- 

 ed. The truth seems to be that Dr. Red- 

 ding does not understand what he so 

 roundly condemns and ridicules. It would 

 seem he has founded his knowledge upon 

 Professor Tyndall's excellent book, which 

 is a published course of popular lectures 

 on the subject. These have been entirely 

 misunderstood by the writer, or wilfully 

 misconstrued. No one who is not a 

 scientific man should criticise a subject in 

 physical science. It is useless to give 

 serious attention to such articles. It is the 

 height of absurdity for a writer to declare 

 that a man like Tyndall has given pub- 

 licity to statements ' Erroneous from 

 beginning to end.' Which is the greater, 

 Tyndall or his critic ? Which is the more 

 competent to deal with this subject? We 

 can only protest against the publication 

 of such nonsense. It is somewhat con- 

 soling, however, to think that in this 

 enlightened age pseudo-scientific cranks 

 cannot do much harm to the progress of 

 science. 



— It IS frequently desirable to have a 

 liquid preservative of the same specific 

 gravity as water. Probably the nearest 

 approach to such a medium is the one 

 recommended to be used with Deane's 

 gelatin medium, having the following 

 composition: — Rectified spirit, i^' oz.; 

 Water, lyi oz.; Glycerin, 5 fl. dr. This 

 can be used as a preservative, or a speci- 

 men may be placed in the medium under 

 a bell-jar until most of the alcohol has 

 escaped, leaving the denser glycerin and 

 water. 



•— At the 36th meeting of the Washing- 

 ton Microscopical Society, held Dec. 22d, 

 Dr. J. M. Flint, Surg. U. S. N., who is as- 

 signed to professional duty of the Fish 

 Commission steamer 'Albatross,' made 

 an interesting exhibition of a collection of 

 foraminifera, obtained during the cruises 

 of the 'Albatross,' from the dredgings and 

 soundings off the eastern coast. The 

 specimens, which had been carefully se- 

 lected and mounted as a type-series on 

 the rotary object-carriers described last 

 year,* attracted much attention, and were 

 greatly admired both for their perfect form 

 and the excellent manner they were 

 mounted. 



The rotary object-carrier is not merely 

 a convenient device for the display of ob- 

 jects, but it is a most excellent device to 

 aid the systematic student. A large num- 

 ber of forms or varieties may be mounted 

 together in the most favorably condition 

 for study and comparison. 



