had not been using ** the spectroscope**  to get the right answer. Was it good for  science's  reputation showing that scientist  could be wrong?  Was it good for for the human race who gained  a better life with the "right; or almost right answer?"

Moseley using the  spectroscope  gathered experimental data  in  x-ray region of the spectrum which was used by Marie curie to find bullets in soldiers bodies in the war I  that would kill Moseley who chose to fight in the war. which he used  to correct the mistakes others made  in the placement of elements in the  Periodic table. He even  predicted that scientist had been missing elements  in this table. 

Planetary atom: Far more  than the finding of empty holes in a table of elements, Rutherford likened this kind of research as stamp collecting.  Moseley had used his spectroscopic data to experimentally check, verify and select the interesting and then current theoretical model offered to explain the nature of hydrogen atomic spectra. The one he chose was the  classic Bohr's picture of a planetary atom. The theory in its simplest form fit hydrogen spectra which didn't last very long before it was modified  with a statistical approach. Still  it was a significant start.

Interesting planetary models were a hot topic in Galileo's timeto some  and certainly to some historians looking for connections.  Galileo 300 plus years ago was struggling with another  . The model  of our solar system.  He was gathering acceptable data using a critical component of a spectroscope-- the telescope in his work. See the last picture  in a collage of  two  replicas of Galileo  telescope made into a spectroscope with prism. 

"Note" Simply replacing the prism with a rock salt grating one could use this spectroscope in Moseley experiment today.

Science was on a roll around 1900's +- 25 years  when Moseley' appeared on the  scientific scene.
In Moseley's time scientist had made enormous  improvements in  scientific instruments that expanded human's sense ,of  seeing, hearing, feeling, etc.,  millions of  times greater  than nature provided.  Example humans  in  Moseley time had to get acquainted with very tiny and very large things at the same time not only single atoms but parts of the atom, electrons, that they could not see directly. The Lorentz radius of the electron, 2.8 * 10 ^-13 cm.. The diameter of the nucleus of hydrogen  proton was in the range of  (1.75×10⁻¹⁵ m)    On the larger size they have had to  start dealing with a universe billions of light years in radius. All this with the new scientific instruments with the little valued spectroscope leading the way.

Gaining perspective  of the instruments that Moseley's had available to work with were improvements in  vacuum technology (from the lighting world), high powered high voltage power supplies (from the power distribute system to light the world), new and more precise spectroscopes (from the analytical chemical world).  Added  to this arsenal was the statistical mathematics from the (business world).

The hottest scientific topics were the discoveries of particles that atoms were made of  electrons protons x-rays and especially  Marie curie's discovery of the enormous energy of the nucleus and Einstein's E=mc^2 were keeping the world of science flat out.

Moseley luck  and borrowed gifts from many others  was his fascinated with  high vacuum pumps , high voltage electron beams and the x-ray grating spectroscopes.

For the latter if we go back in time one of the simplest examples of humans relationship with  spectroscopes, were nature's  rainbows.   Humans could only view  the  sun's radiation using their natural senses. They noted that  exposure to sun meant  sunburns  - later  refer to as ultraviolet radiation, the visible perception  colors light like the rainbow, the sun's warmth  later called infrared radiation.

In our ,new,  world Moseley decided  with help from his adviser to use  a famous senior scientist, Dr.  Bohr, last gasping attempt to use classic mathematical methods to build  a formula to predict   the spectral light coming from  very hot  electron temperature) hydrogen plasma.  Moseley  using this incorrect (in the quantum mechanical  sense) theory decided to count the number of individual protons in atoms using man  made rainbow generators (grating spectroscope made using a large crystals  grown from table salt as the light dispersing element ). His goal was to correct the chemist's catalog of elements and the pieces  they are  made of, appearing (15,000 K)in the Period Table.

Again Quoting from Genesis
 In the beginning "and darkness was upon of the deep'" and "and God  said" let there be light"- In science the rainbow spectroscope was showing scientist the way to  go both big and little with the planetary model.

 -Unfortunately to some?-  humans  could only see a tiny portion of nature's infinite number of colors.
Figure 1 below shows how the visible spectrum connects with the rest of what scientists now call the electromagnetic spectrum. between the names radio frequencies, visible, and gamma rays.
The point here is to note that there is this  limitation in all  our  senses  ; light, hearing, touch, smell, etc. Some would even include common sense in the list?  -Fortunately?- scientist have extended all of our physical senses , perhaps with exception of one, with scientific instruments to expand our exploration of the world. 

The Electromagnetic spectrum--
The figure below may seem complex to many people. The names do not seem connected. This is because as the scientist we're exploring each new radiation they needed a unique detector  they gave that portion of the electromagnet spectrum  a unique name.  In the final cut the only difference is in the size of the wavelength or the frequency of the radiation.

Summary
All elements can be electrically excited to produce a hydrogen like spectra
by  simply stripping off all of its electrons. Moseley did this by shooting electrons generated from  a high voltage source at  a target of the atoms being studied. This generated  a source of  the ionized elements that would produce a  one electron type hydrogen spectra however they will be shifted toward shorter wavelengths in the x-ray spectra due to the higher number of protons in the element.  One can use this spectral shift to measure the element's atomic number, Z (its number of protons). Shown above is the spectrum for hydrogen and the corresponding hydrogen like spectra for the test element being measured in the x-ray region.

Moseley and fellow scientists devised equipment and experimental methods in spectroscopy to  include the x-ray wavelength region of the spectrum, the region necessary for measuring the number of positive charges in the nucleus of atoms. By accurately measuring this unique number (known as the atomic number, Z) for each element they were able to accurately determine the location of an element in the periodic table and even predict empty slots and what the element  might act like . This table is  one of the most important catalogs or spreadsheets for science and engineering.

Moseley's work was far more reaching than the periodic table. His work helped give experimental verification of models explaining what an atom might physically look like, namely Bohr's planetary model of the atom. Below one of a number Moseley's later instrument used to measure the atomic number of the  elements.

Below is what replica of one  of a number of experimental set ups used to in Moseley's  studies.

To the left is Moseley and some of his apparatus.  To the right in the figure above is Moseley's hydrogen like spectra  showing the alpha and beta spectral lines for  varity of elements including Copper, Nickel, Cobalt, Iron, Manganese, Chromium, Vanadium, Titanium, missing element, Calcium.

Below: We generated the atomic spectrum of hydrogen from a low pressure gas discharge tube for readers satisfaction at the simple yet complex spectral features Moseley had to deal with in his experiment. We show what happens when one looks through a grating spectroscope at hydrogen heated by electrons in what scientist call in this instance a gas discharge tube, a very important accessory in science.  Moseley used a source of electron also but bombarded solid  targets to  strip all the bound electron of the atoms. As the electrons rejoined the atom the first ones generated  a line spectra similar to a hydrogen spectra but in x-ray region located by the number of protons in the atom.

 In the figures below---Looking through a transmission diffraction grating at the discharge tube, one will see in the center, the primary non refracted image of the discharge tube. On each side of this center image are the images of the diffracted first and second orders of the hydrogen alpha and beta spectral lines. There are more spectral lines (see figure above) too faint to be recorded by the camera. This was the true of Moseley's  x-ray spectrograms. This spectrum shows the skill Moseley needed to separate  the parts of the spectrum need for the measurement.

Spectra of atomic hydrogen as viewed through a diffraction grating

The diffraction grating in the foreground the arc source in the background