•219
��Auumliig. u Le does, that these crania are all pre-glaclal, anil Qnding ainang them both long uud short skulls, Dr. Eolliuann arrives lnevita>>ly at the conclusion that already in prc-glaclal times Hie men of America had cranial and facial forms widely dif- fercDtiatei] iiilo varieties which have |>ersisl.ed until the present time, in spite of Inpseof time, and change o( eiivirunineut. The persistence of type leads him farther to question the probability of an alteration of race-characters from change of environment, or the possibility uE the development of auotbur, more
��It api^eara to be a law, that, whenever a hj-polhesis of fuDdameatal importance ia iiilro- daced into a science, it is utilized for nil sorU Hii-poses for which it was never intended. B is certainly true of the valence bypotliesis hemistrj-. The conception that the smallest
tides or atoms of the elements differ IVom each other in regard to the number of other atoms with which they can enter into combina- tion, is Hie result of a profound conaiderntion of the facts of chemistry, and its signiScance cun be comprehended only by those who have made a deep study of these facts. The valence Lypoth-
'b is utterly meaningless to those who do not know considerable about chemical substances and their action upon each other. Notwith- atauiUng this, the mere mechanical considera- tions involved in it arc so simple, and can be so readily illustrated, that we find incompetent teachers thrusting tliera ii|)On the attention of li^inners even before any sort of notion has been conveyed in regard to the nature of chemical action, or of the distinction between elementary and com|K>uiid bodies. We need only pick up any one of the small text-books in common use, and, ten chances to one, we stiall Bnd an example of the kind of treatment referred to.
It would l>e difl3cult. however, to find any thing to equal '■The chemists' and students' assistant, or. Kindergarten system of chcmis- Iry," which lias recently been brought to our atteutioD. The author or inventor of this sys- tem evidently thinks that the essential things ID chemistry are not compounds, but formulas ; that, if one can manipulate formulas with sulli- oent skill, he knows chemistry. Now, in or- der to deal with the formulas, it is not at all Decessary to know any thing about the com- poonda represented. A very few simple princi- ples, which .1 child can thoroughly comprehend,
TAt ritrinlttt' aiut ttwItnU' aiililam ; or. Kiniirrn'irlen -vi im »/ <:Atal.ir!/. Ily William Fibvir, New Vork. AulAir.
��are alone required. We are therefore at last in a iwsition to study chemistry without any reference to chemical phenomena. The odor of chlorine and of sulphuretted hydrogen, the activitj- of oxygen, the conduct of acids to- wards bases, need no longer be known to the student of chemistry. Laboratories for in- struction are suiierBiious, All we need is ■ The chemists' assistant.' This wonderful thing consists of a box containing a number of blocks of different shapes. The simplest blocks, which represent the simplest atoms, have but one angle : others have two, three, four, five, or six angles, and represent respectively the bivalent, trivaient, quadrivalent, etc., elements. A col- lection of such blocks by itself is not a very harmful thing, and we can conceive of the blocks being used in connection with a coarse of instruction in chemistrj' without leading to an entirely false notion concerning the things represented. Their use, however, would require the greatest care, as they would be more likely to do harm than good. When we read the author's explanatory words, we first rew^nize the enormity of the system with which he has presented us. After stating in general terms how the blocks are to be used, he says. " For lectures or class illustrations, this system will be exceedingly useful ; for the illustrations on the charts and blackboard will address the eye as well as the mind of the student, and conse- quently will lead to a quicker conception of the subject lectured upon.
"As this system is identical with that of the kindergarten, the young students will be charmed with the various forms which can be made by tho elements, some of which are ex- hibited in the following illustrations."
We then find some illustrations of Chemical i-eactions which certainly do charm the eye of even the old student. The first one represents what takes place when water acts upon calci- um oxide. Oxygen, with its two points, joins two single-pointed hydr(^en blocks, and we have water. Calcium (two-pointed) fits close to oxygen talso two-jxiinled). and we have lime. The change to the hydrate, or, as com- mon people call it, slaked lime, is too abrupt : we therefore have an intermediate stage repre- sented. This is called the ' cracked-up * stage, though, from the general appearauce of the formulas, we are inclined to think that it might better Ije called the ■ exploded ' stage. Final- ly order is restored, and we have a peaceful, symmetrical -looking group, which, we are glad to be told, is 'calcic hjdrate.' The idea of including in chemical equations the intermedi- ate ' cracked-up ' stage, is, we believe, original
�� �
