甚至在19世纪60年代，就已经有了一个相当广泛的元素谱线模式库。
There was a pretty extensive library of spectral line patterns of elements even by the 1860s.
比如，可能会让我们决定有哪些不同的元素可以产生一个有五条不同的谱线的光谱？
We might be asked, for example, to determine what different elements could produce a spectrum that gave 5 different lines.
单谱线多元件透镜可以有不同的外形和材料，有玻璃的，二氧化硅的，蓝宝石的和钙氟化合物的。
Singlet and multielement lenses are available in a wide variety of configurations and materials, including glass, fused silica, sapphire, and calcium fluoride.
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