What kind of Russian orthography is this?

Question

This is a screenshot from Tchaikovsky's Harmony textbook:
(from page 5 of an 1897 edition — link to PDF)

And here is a transcription:

Ученіе объ интерваллахъ.

Хотя предполагается, что приступающій къ изученію искусства музыкальнаго сочиненія, достаточно подготовленъ къ тому обстоятельнымъ знаніемъ элементарнаго отдѣла музыкальной науки, мы считаемъ, однако же, не безполезнымъ предпослать нашему руководству краткое изложеніе ученія объ интерваллахъ, такъ какъ шаткія объ эиомъ этомъ предметѣ свѣдѣнія могутъ препятствовать успѣшному изученію гармоніи.

Подъ интервалломъ разумѣется отношеніе, образуемое между двумя звуками по высотѣ. Въ каждомъ интерваллѣ звукъ, лужащій ниже, называется основнымъ. Наименованія интервалловъ соотвѣтствуютъ латинскому обозначенію отношенія, образуемаго между верхнимъ звукомъ и основнымъ.

Is this the pre-reform orthography? If someone is learning modern Russian, how difficult will it be to understand such paragraphs?

Answer 1

Yes, it's Russian in the pre-reform orthography. The reform was in 1918, so this is just hundred-year-old Russian. It's easy to understand, just like it's easy to understand hundred-year-old English. The main difference from the Modern Russian is the use of some letters that were removed from the alphabet in 1918. They were replaced by different letters. In order to convert a text like this into the modern Russian orthography, you have to follow three steps:

1. remove every ъ, "hard sign", at the end of words, e.g. объ → об;
2. Replace the obsolete letters with modern ones:

ѣ → е, e.g. разумѣется → разумеется

i and ѵ → и, e.g. ученіе → учение

ѳ → ф, e.g. Ѳедор → Федор

Note: Your sample passage has no ѵ or ѳ, but these were also used, albeit rarely. 3. substitute the adjective endings: -аго → -ого, e.g. образуемаго → образуемого

-яго → -его, e.g. синяго → синего

Also, the endings -ыя, -ія → -ые, -ие, and the pronoun ея → её. These are also not found in you sample.

That's all. You'll end up with Modern Russian orthography. To make it even simpler, there's an online converter, which can convert whole passages to and from the two orthographies.

UPD. I just noticed that your sample does have an adjective ending in -ія, thus шаткія → шаткие.